Help With A Battery Question

[Wassernaut]

Can someone help me with a battery question?

I hope all will excuse this not being associated with flashlights - but it is a battery question. I am at a loss to find bonafide knowledgeable people to answer an important question (to me) .

I depend upon a complex power wheelchair daily. It's a high dollar ($16,000.00) chair, with multiple motors and functions. My question is about the charging of the large gel cell batteries.

I have been told specifically by wheelchair specialists that I should charge the chair every night, no matter what the charge level . This goes against all I've ever heard about battery charging. The chair has two large 12 volt gel cell batteries. I can usually get by with charging the chair once a week, and the indicator still shows I have about 1/4th of the charge left after using the chair all week. Some days I'm not able to use the chair much at all - they still tell me to charge it every night. They say that I will get the absolute longest use out of the batteries (very expensive to replace - $200.00) by charging them every night. I normally end up charging the batteries about every four days, with about 1/2 of the charge used.

But - I hear on the forum of many who must buy new batteries every year or so using this advice. I used my last power chair for five years (still have it) and the batteries are still fine. I charged the batteries (same type as in my new chair) only when they needed it - about once per week.

Since the chair and the batteries are so expensive it's very important that I get the longest possible use before having to replace the batteries.

So, do I listen to the "experts" or keep doing what has worked for me?

Your thoughts -

Larry

 

[BVH]

I'm by no means an expert but here's a great battery facts web page. If your batteries are the "deep cycle" type, then they are made to discharge deeper than conventional sealed lead acid (SLA) and it is probably ok to not charge them each night. My reading on conventional SLA's (non-deep cycle) indicates they like to be charged immediately after use.

windsun.com/Batteries/Battery_FAQ.htm (add the "www.http://.")

 

[Mr Happy]

This might not be a simple question.

I think that gel cell means the batteries are a kind of lead-acid accumulator. Now some lead-acid batteries such as the ones in cars do not like to be deep cycled. They apparently last much better if they are kept topped up all the time without being allowed to run down. On the other hand they should not be seriously overcharged either.

There are other kinds of lead-acid accumulator that are better able to withstand being discharged before recharging, but I'm still not sure if that is the best way to prolong their life.

So the best answer in your case might depend on the specific installed batteries and the specific design of the charger.

Maybe they advise you to charge it every night because they don't know the particular usage pattern of every individual and some people might be in danger of emptying the batteries in two days of use? By advising everyone to keep the batteries topped up they might be reducing the risk of anyone draining the batteries right down.

I think that if you replaced the lost charge every night but did not overcharge the batteries beyond that, then it would be best for the batteries. But I don't know how well the specific charger avoids overcharging.

 

[Wassernaut]

Mr. Happy -

I explained my typical usage in detail on the wheelchair forum before receiving the advice to charge daily. Also the charger is an off board charger made specifically for this chair (battery), and is quite expensive and supposedly very sophisticated as to its battery conditioning and protection against over charging. I am beginning to be sold on the 'every night charging' technique.

Larry

 

[UnknownVT]

Be sure of the battery type -

This seems a good link (although it is a commercial site) -

http://www.batterystuff.com/tutorial_battery.html

" It is very common for individuals to use the term GEL CELL when referring to sealed, maintenance free batteries, much like one would use Kleenex when referring to facial tissue or "Xerox machine" when referring to a copy machine. "

Battery University is also a very useful site.

Wikipedia on Deep cycle battery says:

" While a deep-cycle battery is designed to discharge down to as much as 20% of its charge capacity over several cycles, companies recommend that a hybrid battery not be discharged beyond 50% of its capacity. [1]. "

That link in the Wikipedia quote points to the same wind-sun.com FAQ given by BVH

So it would seem that even from my limited knowledge and this minimal research - Gel Cell batteries do NOT like deep discharges
- there does NOT seem to be any benefit in discharging the battery to low levels, it seems the opposite, deep discharges can damage the battery.

 

[Probedude]

So, do I listen to the "experts" or keep doing what has worked for me?

Your thoughts -

Larry

Do both.
- charge as often as you can

SLA's (even flooded lead acid) can be float charged forever. The deeper the discharges, the less number of cycles the battery lasts. Deep cycle batteries are designed to give more cycles to a particular depth of discharge than a non-deep cycle battery - but they too still benefit from shallow discharges.

Sounds like if you've gotten 5 years out of your packs you current regime isn't bad for them BUT 5 years is pretty good life even for well cared for SLA's so do budget for a new pack in the near future. It also sounds like your charger is a very good one - it isn't baking your batteries each time you hook it up.

Dave

 

[Wassernaut]

Thanks - Unknown, for some valuable info and advice. I knew this was the place to go for some legit advice on my questions. Larry

 

[SilverFox]

Hello Larry,

Over 80% of lead acid battery failures involve sulfation of the plates. Sulfation initiates when the battery drops below about 12.4 volts. Please understand that this voltage is a resting voltage measured at room temperature. After use, it can take several hours for the battery voltage to stabilize, but I think you can get a good idea of where you are after around an hour or so.

I would suggest that you borrow a volt meter and use it to discover where 12.4 volts is on your remaining power indicator. Now you have a target voltage. In use, your batteries will drop below that, but after a rest, if the voltage does not rebound over 12.4 volts, charge them up.

On the other hand, if this seems like too much fiddling around to do, charge them after every use...

Tom

 

[Anders]

Hello Wassernaut.

Here is also a good place to find useful information about 12 Volt lead acid batteries.


Anders

 

[Wassernaut]

Wow! Many thanks to all Flashaholics replying and helping me with great info. I was hoping Silver Fox would drop by with his excellent expertise, thanks Brother. And thanks to Anders, the link provided some interesting and very helpful reading. Again thanks to all for helping a bonehead with a need for some help with an important quandry. My power wheelchair is my independence, allowing me to retain my freedom. - Larry :thumbsup:

 

[Bones]

...
I am beginning to be sold on the 'every night charging' technique.

The consensus certainly appears to be that lead-acid batteries last longest when kept as close as possible to a fully charged state.

The trick, apparently, is to keep them from overcharging whilst applying frequent charges, which your charger sounds very capable of doing.

Another reference for lead-acid battery queries:

Car & Deep Cycle Battery FAQs 7.1

...
Over 80% of lead acid battery failures involve sulfation of the plates.

FAQs on sulfation:

16.1. How Can I Tell If my Battery Has Permanent Sulfation?

16.2. How Do I Prevent Permanent Sulfation?

16.3. How Do I Recover Sulfated Batteries?

16.4. Where Can I Find Additional Information On Sulfation?

Roll on ...

 

[Turak]

Hi Wassernut,

I have A LOT of experience with SLA batteries.

In general......a SLA type battery will last many more cycles if you DO NOT deep discharge them. They also typically do not suffer any ill effects from repeated shallow discharge/recharge cycles. They actually prefer shallow discharge/charge cycles as opposed to full discharge/charge cycles when it comes to overall life. They are almost a complete opposite of a Ni-Cad/NiMH battery when it comes to charging/discharging.

Almost all SLA batteries (i.e. UPS's, wheel chairs, etc.) are actually of the AGM (Advanced Glass Matt) variety now a days and do not actually have liquid in them like a typical car battery, referred to as a 'flooded lead acid' battery. What they have in them is a fiberglass type material that is soaked with an electrolytic fluid and used as the separator or part of the separator. That is one of the reasons that they can be used in any orientation.

They also 'prefer' being kept fully charged or on a float charger. You can trickle charge them for MUCH longer than almost any other type of 'standard' type battery.

They tend to die because of 'extended over charging' which over time (i.e. 3-5 years) ends up drying out the electrolytic soaked fiber seperators. Most UPS's are guilty of this problem. I have seen AGM/SLA batteries last as long as 10 years if not over charged or deep cycled.

If you shallow cycle (i.e. less than 50% discharge) them and recharge them, they may last up to twice as long if not a little more compared to doing 'full' discharge cycles on them.

Call and talk to ANY reputable electric wheelchair dealer and they will tell you to recharge the chair every night.....which is totally correct. I would actually carry it one step further and say to charge it up every chance you get.

The problems with plate sulphation generally applies to 'flooded' lead acid batteries much more than to 'sealed' lead acid (SLA) batteries. I would not recommend wasting any money on desuphinator devices to try and rescue SLA batteries. Hehe, believe me, I have tried. I have even designed my own desulphinator circuits, which work reasonable well for 'flooded' lead acid batteries, but not for SLA batteries or even 'gell' cell type batteries. As I stated above, most SLA batteries dry up instead of the plates becoming sulphinated.

 

[Wassernaut]

Again - Thanks Bones and Turak for some very good information. - Larry