AA or C-cell NiMH, that is the question...

I am about to purchase a Sangean PR-D15 AM/FM radio. It runs on AC and has the option of a 6 C-cell battery backup. It also features a built-in charger for NiMH batteries (a feature I really liked, especially in case of power outages). I already have and use many AA and AAA Eneloops and a couple of chargers. Also, for years I've been running a Streamlight Waypoint LED spotlight (used nightly), which takes 4 C-cells, on AA NiMH's using Eneloop adapters, so I'm familiar with those.


My questions are:
1) would I be better off using AA to C adapters or just getting 6 NiMH C-cells since it has a built-in charger?
2) I assume the built-in charger would work OK with AA's in adapters (electronics is NOT my forte)?
3) If NiMH C-cells would be the best option, which ones? FYI, the normal usage would probably be 80% AC and the rest on batteries.


Thanks in advance for any assistance. You folks have helped a lot of people over the years, me being one of them (the Streamlight and AA adapters setup was one), and you're highly appreciated.

I would be rather tempted to modify things for lithium ion power myself depending on how much space you have a 2 or 4 cell 18650 setup with balancing/charging support as it could afford you more power and runtime and the voltage of 2 series cells is within range.

Lynx_Arc said:

I would be rather tempted to modify things for lithium ion power myself depending on how much space you have a 2 or 4 cell 18650 setup with balancing/charging support as it could afford you more power and runtime and the voltage of 2 series cells is within range.

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Well, thanks, I guess. What you said is all Greek to me, so that probably ain't gonna happen. Like I said "electronics is NOT my forte".

If you already have the AA to C adapter and AA batteries, then just give it a try.

It would also be important to know whether the built-in charging function switches off reliably or whether the batteries only boiled to death over time?

sbj said:

If you already have the AA to C adapter and AA batteries, then just give it a try.

It would also be important to know whether the built-in charging function switches off reliably or whether the batteries only boiled to death over time?

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I'd have to buy the adapters but they're a lot cheaper than NiMH C-cells. I can get a 6-pack of LAMPVPATH adapters brand for $7.

I have no clue on the charging function other than it supposedly goes on/off as needed. I did read a few reviews that stated the reviewer uses rechargeables and loves it, for whatever that's worth.

First off, I would say that since your radio works with size C batteries, use either Alkaline or NiMH. If you use any NiMH battery. remember to switch the battery switch to NiMH from the Alkaline position. It should automatically compensate for the lower voltage and also recharge them too. And from your other question on this site, I would say Amazon Basics Size C NiMH....Like I said before, they have been running in my Sony radio for almost a year. Will do an update review in June/July when the year is over. Since the radio recharges them in series (not each one at a time) you would have to take them out and do a refresh cycle on them. I'm guessing every 2 years. You would also need a charger to accommodate them.

Second choice would be using the size C adapters with AAA or AA NiMH cells. Just remember that not all the cells will charge correctly due to the small internal differences within the cells. Also you will not have the same capacity the size C NiMH cells. Once in a while you will have to take them out and do a refresh cycle with an external charger. From your other use of these, I would recommend this choice for you.

Third would be the lithium Ion type batteries. This is gonna get a little complicated. Remember that these would have to be run on the Alkaline setting. That would turn off the charging system in the radio. NiMH charging is different than Lithium. You would have to get a charger that would accommodate them. 18650 types would probably need some tape around the battery since these are only 18mm in diameter and Size C are 25-26 mm in diameter. If you wanted to use lithium ion batteries without the diameter spacer I would try 26650 lithium ion. 2 of them would give you 8.4 volts Max, 7.4 volts min. (The total voltage with Alkaline is around 9 volts., The total voltage with NiMH would be around 7.2 volts.) If you put 2-26650 batteries in 1 row, you would have to get some sort of length spacer. Also, I would also use protected cells which are going to increase the length of the battery around 4-5 mm. Protected batteries are protected from all the nasty things that cause lithium battery accidents. (Most of them) This would leave 2 of the lithium batteries in a row and then some sort of electrical shorting spacer around 10 mm long and 25-26 mm in diameter. I have heard that some people use Neodymium Iron Boron magnets to take up the space and conduct the power. I have not tried this. A wad of aluminum foil might work too. The next row of batteries would be C adapters with dummy (shorting) AA or AAA's in them. Once again, make sure the battery switch is in the Alkaline position. You don't want to charge lithium batteries inside you radio, since the radio isn't made for this type of battery. There are many type sizes of lithium ion batteries. I have written about 2. You could also use 1 26650 in each row and purchase a dowel (3/4 to 1 inch in diameter) with a shorting wire around a screw in both ends to take up the space. That dowel would be approximately 80mm if my math is correct.

Forth would just use Alkaline types. Since you stated the 80/20. That is not much time on the batteries. So going rechargeable may not be the best economic solution. That is unless you're just trying to save the dump sites. The only problem with Alkaline is the possibility of leakage and damage to the radio. Make sure the battery setting to set to Alkaline.

The owners manual that I got online for you radio states recharging size C NiMH batteries takes 8 hours for 3500 mAh. The Amazon Basics will take more time because they are rated for 5000mAh. Hopefully there isn't a time out on the charger. If there is they may not charge up all the way. If you use your adapters, then it will take a shorter time since the AA Eneloops capacity are less than 3500mAh's.

Since the charger is going to charge the cells as a group and not individually, you would be better off using a separate smart charger.

Eneloops or Fujiloops in spacers is a good option, runtime will be shorter than with NiMH C's but you will have lower self discharge and lighter weight.

If you want longer run time, Soshine low self discharge NiMH's are good.

If you want to convert to Li-ions. you can get a couple of 3C to 18650 or 3C to 21700 adapters and run protected Li-ions - it's important to use only protected cells, since you will have 2 in series. 21700's have about the same capacity as 26650's which may be a little too fat to fit in place of C cells.

I have had issues using C-adapters with AA NiMH batteries when trying to physically remove the adapter from devices which have individual contacts for each battery where the adapter is inserted perpendicularly into these contacts. I have not had any physical issues using C-adapters in tubular devices where the batteries are inserted in-line and captured with a screw-on end-cap.

Since AA and C batteries are the same length, the C-adapters are usually slip-on hollow sleeves where each end of the AA battery is exposed and the original battery contact areas are used for the connections to the device. My C-adapters allow either end of the battery to be inserted first but do not allow the battery to be pushed all the way through the adapter

In my case, using my particular C-adapters in devices where each battery is inserted perpendicularly into its own set of contacts (with a strong spring on the negative terminal and a pronounced bump for a positive terminal), creates the problem where no matter which way I inserted the battery into the adapter (or oriented the adapter in the device), the device's "negative terminal spring" or "positive terminal bump" hangs-up on one or the other end of the adapter when I try removing it and I have to slip something thin and stiff between the adapter and battery contacts to remove the adapter.

It is more of a issue than might seem from my description above because inserting a thin item also wedged the adapter tighter, jamming it up enough during battery removal to eventually cause the battery contacts in my weather station which had a particularly tight battery compartment to fail by breaking the electrical connection to the circuit board. I reverted back to using primary disposable batteries after repairing the damage.

I might try using appropriately sized Tygon Tubing or Rubber Hose sliced into short pieces (maybe even cutting a split in the short pieces if they are too tight for the battery) and use these as spacers near each end the battery instead of the C-adapters to bring the AA diameter up to a C diameter. I do this now with O-rings near each end of a battery when using 18650 Li-ion cells in 21700 compatible lights that have long enough springs to accommodate a slightly shorter battery and it has worked adequately. The O-ring spacers do not produce the rattling sounds when shaken like the plastic hollow spacers sometimes do.

When battery capacity is not an issue, D-adapters with AA batteries have physically always worked well for me even in devices where each battery is inserted perpendicularly into its own set of contacts. This may be because since D-cells are longer in length than AA-cells, most D-adapters enclose the entire AA battery which requires additional secondary battery contact areas to be built into the adapter (but unfortunately these additional contact areas also undesirably increases the overall electrical resistance for the battery/adapter combination).

I have not tried recharging AA batteries while they are inside C-adapters (or D-adapters) using the device that they also power, but an issue to consider would be the charging current supplied to the batteries by the device. NiMH C-sized batteries (~4000 to 5000 mAh) have about twice the capacity in mAh (milliamp hour) as AA-sized batteries (~2000 to 2500 mAh) and the usually recommended "mA (milliamp) charge rate" for NiMH batteries that I have seen from charger manufacturers is "0.3 x C" to "1.0 x C" (where C is the Capacity of the battery in mAh). So the concern would be that the default mA charging rate for a device designed for C or D sized batteries could be too high for AA batteries.

Batteries in devices containing multiple batteries could be in grouped in a "series", "parallel", or a "series-parallel" configuration which would affect how they are charged by the device. I have flashlights that charge 3 NiMH batteries in "series" which is not ideal (since each battery will eventually be charged differently) and prefer using a multi-cell analyzing charger which monitors and charges each battery as a separate individual so I can keep track of their capacities and internal resistances as they age. Most NiMH chargers accept AA and AAA cells but only one of my NiMH chargers will accept C and D cells and another requires a special adapter for C and D sized cells, so that is something else to also consider.

Fortunately NiMH batteries are relatively inexpensive and are also not very dangerous, so it is easy to experiment without worrying about the consequences of a failure, which could be catastrophic if using Li-ion batteries.

Firstly, WOW, as usual the folks at CPF came through. Thank you very much. I'm sure others will also glean knowledge from this thread.

Secondly, and based upon what I've read here, the equipment I have on hand, money, and my own (very) limited knowledge, I've decided upon the following. I'm going to use Eneloop AA's in adapters. I have two chargers, one is an Eneloop BQ-CC55 and the other is a La Crosse BC700-CBP. BTW, the latter has a refresh option. I don't want to have to get different batteries, i.e. C-cell NiMH, and then a another charger on top of it, just to run a radio. That spotlight I mentioned above has been working just fine on AA's in adapters (FYI, informally, I found the run times between those and alkaline C-cells to be roughly the same). I just wasn't sure, for some reason, if I could do that with the built-in charger in this radio. I should've realized that the voltage is the same. Well, ignorance breeds fear, and now I'm no longer as ignorant

NiMh cells are in everything we use daily and disposables, alkaline or Li-Ion, in items that just sit most of the time and/or items that are exposed to temp extremes. I do check these periodically (1st day of spring and fall) using my INNOVA 3320 DMM. This seemed like the best way to go when I first got into rechargeable cells. Buying many C and D NiMh cells (on top of the AA's and AAA's) and an expensive charger just wasn't cost effective.

I should've mentioned this earlier, I emailed Sangean to find out what the charge rate is for the PR-D15. If I hear back from them, I'll post it here. Worst case scenario, I'm stuck with 6 adapters and have to buy 6 C-cell NiMh. Not the end of the world.

Any-who, once again, thanks to all of you and I'll keep you posted. I'm also open to any further advice as well.

Good day.

The following is in reference to the charge rate concern. When I hear from Sangean I'll post it.

Macgravy said:

The owners manual that I got online for you radio states recharging size C NiMH batteries takes 8 hours for 3500 mAh. The Amazon Basics will take more time because they are rated for 5000mAh. Hopefully there isn't a time out on the charger. If there is they may not charge up all the way. If you use your adapters, then it will take a shorter time since the AA Eneloops capacity are less than 3500mAh's.

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Maybe I'm calculating it incorrectly but to me it seems my BQ-CC55 has a higher rate.

I have the pr d5 model without the recharging feature and usually use the eneloop c to aa adapters with eneloop batteries and have been very pleased, especially knowing that they won't leak and destroy the radio. I have used c batteries for extended play since their capacity is like double but don't leave them in the radio when not in use. Don't trust alkaleaks! If I had the newer rechargeable model, I would go with the lithium batteries because that's what I use in most of devices that aren't aa/aaa. But one factor that keeps me using the adapters is the savings in weight. The radio is considerably lighter when using aa's and that's important for me when toting radio on bike or in pack.

You are welcome. Anytime. From looking at https://eneloop.panasonic.com/en/products/charger-bq-cc55.html for your Panasonic charger, if you using the 1900-2000mAh AA batteries: 1-2 batteries takes 1.5 hours, 3-4 batteries takes 3 hours. If your using the 2400-2550 mAh AA batteries: 1-2 batteries takes 2 hours, 3-4 batteries takes 4 hours. If you divide what your radio manuals states: 3500/8 = 437.5 mA charge rate. I probably wouldn't use AAA's for the radio unless you bought C adapters that used more than 1 AAA battery. You can figure out the charge rate for you BQ-CC55. I believe that the charge rate will change with the number & type of batteries your recharging.

I too have a La Crosse BC-700 charger. Along with an AccuPower IQ-338XL for the C's & D's, along with a couple of Lithium Ion batteries. They have served me well.

The reason that you are getting around the same runtime from the Alkaline's and the AA NiMH batteries is most likely due to the current draw in the light. The higher the draw really starts to decrease the Alkaline's runtime in comparison to NiMH type batteries.

Macgravy said:

You are welcome. Anytime. From looking at https://eneloop.panasonic.com/en/products/charger-bq-cc55.html for your Panasonic charger, if you using the 1900-2000mAh AA batteries: 1-2 batteries takes 1.5 hours, 3-4 batteries takes 3 hours. If your using the 2400-2550 mAh AA batteries: 1-2 batteries takes 2 hours, 3-4 batteries takes 4 hours. If you divide what your radio manuals states: 3500/8 = 437.5 mA charge rate. I probably wouldn't use AAA's for the radio unless you bought C adapters that used more than 1 AAA battery. You can figure out the charge rate for you BQ-CC55. I believe that the charge rate will change with the number & type of batteries your recharging.

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I dug up 6 Eneloop Pro AA-cells. They're rated at 2550 mAh. 2550/4=637.5 mA charge rate for the BQ-CC55. 200 mA's higher that what the radio would be (437.5 mA), if I'm figuring this out (and understanding it) correctly. So, I guess it should be OK :thinking:.

I think someone makes a 4 AAA to C-cell adapter but I'm not using AAA's. That would take 6 adapters and 24 AAA-cells. I'm thinking it would be cheaper to just buy 6 NiMH C-cells in that case.

Thanks for the info on the spotlight. I have an old thread on it here somewhere. IIRC, that's how I got into NiMH's in the first place. We're in rural west central Wisconsin. We also have dogs that have to go out at night. I got the spotlight to scan the property for critters before letting the dogs out, which has paid off more times than I can count, and to keep tract of the dogs. The Eneloop's, adapters, and the La Crosse BC700-CBP paid for themselves in a few months. The rest is history...

BTW, I have a couple Eneloop Pro AA cells that my BQ-CC55 will not charge. It will flash red. They will charge in the La Crosse. Weird.

ledbetter said:

I have the pr d5 model without the recharging feature and usually use the eneloop c to aa adapters with eneloop batteries and have been very pleased, especially knowing that they won't leak and destroy the radio. I have used c batteries for extended play since their capacity is like double but don't leave them in the radio when not in use. Don't trust alkaleaks! If I had the newer rechargeable model, I would go with the lithium batteries because that's what I use in most of devices that aren't aa/aaa. But one factor that keeps me using the adapters is the savings in weight. The radio is considerably lighter when using aa's and that's important for me when toting radio on bike or in pack.

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A lot of folks talk about alkaline cells leaking. Since I can remember (I'm over 60 BTW) I had them leak only once, in a Terralux Lightstar 80. That's probably (I'm guessing here) because it sat in my truck through winter and it get's cold here. I also haven't used anything but Energizers in years either because I've gathered that they are a very high quality battery. That was the incident that got me turned on to Energizer lithium cells for outdoor use (thanks again CPF people). With that said, I agree with you, why take the chance, especially with expensive (for me) electronics.

You are correct that the charge rate for the Panasonic charger would be OK...In fact, from the manual for 2 batteries would be 2550/2 or 1275 mAh. Much higher but still OK for those cells. But then that is only recharging 2 at a time instead of 4. Just remember the charge rates that you and I are coming up with are approximate. Until you hear something from Sangean, go with these calculated rates.

You are also correct about the number of AAA cells used. That math is easy and I have done it many times because I always count the number of cells needed. I do have some of those adapters, but only in case of emergencies out here in earthquake land.

It may be time to do a refresh on those Eneloop Pros that don't charge well. Chargers can be finicky at times.

The current capacity of NiMH batteries vs. Alkaline starts to shine over the 500 mAh (.5 A) current. Ya, it's kind of a pun.

Macgravy said:

It may be time to do a refresh on those Eneloop Pros that don't charge well. Chargers can be finicky at times.

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I did try that and got nada, still flashes red in the BQ-CC55. I have those marked and just use them in a mouse and a sound bar remote. Hey, drive 'em till they drop...

Macgravy said:

The current capacity of NiMH batteries vs. Alkaline starts to shine over the 500 mAh (.5 A) current. Ya, it's kind of a pun.

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Ya, it's kind of a bad pun, but I like it :twothumbs

OK, got the radio yesterday and set it up. I used those Eneloop Pro's and the new adapters and so far, so good. The radio, itself, is very nice and has good sound and volume for a portable.

One thing I noticed was, after running on batteries for a couple of hours, when I plugged it back in, it charged up for a bit. I'm guessing that anytime the batteries aren't 100% the charger will top them off. One thing I don't care for, and really it's insignificant, is the time can be manually set or auto-adjusted off a RDS station. RDS in my area is not that great and often the time is off. A nicer feature would be, instead of RDA, a linkup to the atomic clock. My daughter gave me a La Crosse atomic wall clock with day/date, indoor/outdoor temp, and moon phase and I love it.

If anything out of the ordinary occurs, I will mention it here. Thanks again to everyone for all your help. It's always a (useful) education when I come here. Th-th-th-that's all folks!