Review & dissection of magicshine battery mj-828

Executive summary – for the regulars

Nice new battery case, might even be water resistant.

Same old battery inside

Note this is the deal extreme case, NOT the replacement battery from geoman or various other sellers.

Background

I bought a magicshine bike light mj-808 with an updated battery back that appears to be better designed & possibly even rainproof. I am one of those people that pulls new stuff apart to see how it works & this was no exception

The battery pack is known as mj-828. It is not listed separately on DX but there are a few listed on ebay.

The same battery pack is used in the similar light with a different housing & clip but the extra $20 did not seem worth it to me.

As I understand it, there are four issues with the magicshine batteries:

· Getting wet
· Overcharging
· Excessive discharging
· Defective cells

Makes them sound like gremlins – don't get them wet, don't feed them after midnight.

What really got my attention was this Material Safety Data Sheet "At contact of electrolyte with water traces of hydrofluoric acid may be formed".

Despite the focus on flames, personally I am far more concerned about any possibility of coming into contact with hydrofluoric acid, so a waterproof battery pack was high on my list of priorities.

The before shots

The promotional shots are as good as any.

Getting it apart

Getting it apart was easy. The end caps are held on by two external allen head bolts. Undo these, trying not to lose the nuts or washers, and both end caps simply slide out.

Initial impressions reinforced the build quality you have come to know and love from these lights – in my case there was a piece of foam caught under the o-ring which would have done a nice job of wicking water straight past the seal and nothing to indicate any grease on the o-ring. It seems that o-ring grease is as uncommon as thermal paste in these Chinese factories.

The housing is simply a tube of aluminium

One side is flat while the other 3 have a curve, so the caps only fit on one way.

The battery pack itself

Call me optimistic, but I was hoping that having put the battery pack in a better case that they might have paid some attention to the battery itself. I was surprised to see a centre tap wire & dared to hope that it might possibly be used for balancing.

Alas it appears this was there on the old packs and is only used for over/under voltage shutdown and doesn't perform any balancing see this thread on mtbr at post 87

To my untrained eye the PCB appears to be the same

On the plus side there is nothing to indicate that the battery is any worse than the original – yes I am an optimist.

The volt meter

One of the pieces of marketing on this pack is that it has a backlit lcd display showing volts & a little fuel gauge with 5 steps. To my way of thinking this "feature" is completely useless

· When I mounted the battery on my bike, there was no easy way to see the lcd
· The led on the back of the light changes from Green to Blue to Orange to Red as the voltage drops.
· It displays voltage of the pack, which doesn't tell you if the pack is out of balance
In case you care, here is a pic of the volt meter circuit board

I voted with my soldering iron & removed it. Oops there goes my "warranty" but it means there is one less thing to go wrong & there is now a convenient spot to put a switch to turn the battery off rather than having to unplug it from the lighthead.

It probably sums up the build of the pack that when I removed the volt meter I discovered they fitted strain relief to the cable to stop you pulling it out of the end cap. Unfortunately the strain relief they chose was a steel circlip – two nice points of thin conductive material – just what you don't want putting pressure on you power lead, so I removed that too and replaced it with a small plastic zip tie.

Putting it back together

It's just a reverse of the disassembly steps right? After spending a couple of fruitless hours trying to re-insert the end caps & o-rings, contemplating replacing the o-rings with silastic & general frustration, I had a closer look at the end caps.

Each one has four screws –if you look carefully you will see them hidden under round pieces of plastic. The end caps are actually two parts that squeeze the o-ring, so once you take the cap out, it won't just slide back in.

Instead you have to loosen the four screws till they are just holding the pieces together, lubricate & re-insert the o-ring, insert the end cap & tighten the four screws. When done this way it was a work of minutes.

The observant will see that these screws introduce eight potential leak points & a piece of glorified sticky tape is unlikely to last the distance. The bodger in me wanted to fill the heads with silastic, but I know if I ever want to reassemble it again, silastic in Phillips head screws is a PITA. For now I have kept the plastic dots, but will need to find a better solution

Conclusion

The new housing addresses one problem – waterproofing, but the other three remain. Overcharging & discharging can be addressed with care and a better charger. Time and monitoring the voltages of the individual cells will reveal defective cells.

Welcome to the Chinese lottery – you pays your money and you take your chances

You are overexaggerating balancing of the cells - you have standard over/under voltage protection the same as in the millions of battery pack's in cameras, tools, bike lights, etc. Nobody is balancing any li-ion cells in 1s2p / 2s2p even 2s3p battery packs and they work for 300-400 cycles without any problem.

Why ? Because they are made from the same cells and the current draw is usually lower than 0,5C or even 0,25C - simply there is no need for that.

You may be right although that was not my intention.

There are many magicshine batteries that died in less than 300-400 cycles, some in significantly less cycles. Some of these are out of balance, but as I understand it, this is a symptom rather than the cause of the problem. Instead the cause would appear to be defective cells.

Thanks for your comment

Yep, I think that low quality (for certain cheapest available) cells are the main cause here.

Thanks for the review!

As for the voltmeter's utility, I keep mine strapped to the stem, which makes it quite handy. (Got a couple old-model batteries slung under the top tube for long rides, but I run both headlights and a taillight off the new battery for my commute -- ~3 days worth of juice, but I charge nightly.)

Also, the voltmeter + the overvoltage protection = knowing when it's out of balance. If it only charges to 8.2V, you know one cell is ~4.25, the other ~3.95, better open it up and balance it with the ol' hobby charger -- and if it goes back low in a hurry, rebuild it.

Of course, you can use a voltmeter on the connector to check for imbalance, just like the old ones, and if you can't (or don't want to) mount it where you can see it, I can see why it's pointless, but I'm glad to have it.

Thanks Benson. The voltmeter is a personal preference thing, but I am glad you have found a use for it.

Are you sure the battery pack is accurate? What I didn't include in the review was that mine was showing 8.2v fully charged while my multi-meter was showing 8.4v. Sure my multimeter could be wrong, but at least I know its consistent

One thing I should have done before remiving the voltmeter is chech the volts at which the led on the switch changes colour. I caught it changing from Green to Blue the other day and measured 8 volts, but don't know when it changes to Yellow, Red, or god forbid flashing Red.

Given that you charge nightly, I am guessing you don't see much of yellow or the other colours.

In theory these are Green (75% - 100%), Blue (50% - 75%), Yellow (25%-50%), Red (10% - 25%), Flash red (less than 10%) but it would nice to know what the voltage actually is

They are using very low quality sens resistors, in that case the difference between real values and this what you can see on the MJ-828 display may be greater than 10%. The same goes with the MJ-808 Updated version 4 color battery indicator it's common that one of the colors is dominating in every lamp - but it can be the different one .

find_bruce said:

Welcome to the Chinese lottery – you pays your money and you take your chances

Click to expand...

MJ-828 Battery Pack.

Hi, I'm new to the forums. I've come seeking knowledge. I bought one of these battery packs last year to use with a Magicshine P7. It was about £30 on eBay. I charged it, used it once, charged it again, unplugged it from the charger the next day and found that it was completely dead.

There was a lot going on in my life at the time, and I didn't want the hassle of going through eBay. So I cursed it, chucked it in a drawer and forgot about it. I just found it again and I'm wondering if it might be a simple fix.

My soldering skills are good and I have a basic soldering kit - I used to be an thru-hole solderer - but my electronics knowledge is iffy, especially SMT. Can anybody suggest a starting point?

Thanks, Tib.