# Shorted Batteries



## EVfun (Mar 14, 2010)

Pretty much any lead acid battery that has a resting voltage under 11.7 has been damaged. How much capacity those 2 lost is not easy to estimate, but they have been hurt. They may be usable, depending on requirements.

The one resting at 12 volts may have survived. If it got to hot during the "discharge test" it may have lost some capacity or suffer from increased internal resistance.

I would charge them individually and stay present while doing so. Watch the voltage and current and make sure they behave like batteries during a charge cycle. Load testing them after that is the only way to determine the extent of damage.


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## claeton (Apr 18, 2010)

Thanks for your advice!


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## rmay635703 (Oct 23, 2008)

claeton said:


> OK, we made a very stupid mistake, which we are referring to as the "industrial accident".
> 
> Three 12V lead acide batteries (the kind used in electric minibikes) were inadvertently connected in series with no load, a complete short circuit.
> 
> The voltage on the three batteries now reads 10v, 10v, and 12v. How can I tell if these batteries are toast or not (without blowing up my garage


Anyway Is the 10v after recharging? If not, you have killed them by not immediately recharging. (you can draw a fla almost flat if you immediately and rapidly recharge it with a dumb charger, although it will loose capacity)

I usually dump charged batteries I brought too low or reversed coupled with a 10amp smart charger. Then I would slow charge from then on until the battery came back.

Anyway We used to direct short batteries with a tire iron to load test, so I guess I am not much worried by heavy loads on FLA. The gassing and physical damage is usually visually very apparent, if not they are likely fine.

If you ever do that again pop all the caps and just recharge them as normal, if all the cells start to bubble once the battery reaches full charge they are fine, they just probably have lost 30% of their full capacity which does come back if you treat them right from now on and do a lot of light discharges coupled with multiple balancing charges.

If they are shorted internally a normal slow charge car battery charger normally can't ignite or harm them (a dumb charger might pop a fuse or be damaged if the volts are too low), so long as you watch the batteries a while to see if they bubble and charge in every cell. If they don't or draw WAAY too much juice you will know right quick.

FLA is the most durable and selected battery for a reason.


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## claeton (Apr 18, 2010)

These are SLA batteries, and we have not attempted to recharge them yet. The voltages are the ones measured right after the "industrial accident".

Any precautions I should take while recharging these SLA batteries the first time after shorting them out?

Thanks.


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## rmay635703 (Oct 23, 2008)

claeton said:


> These are SLA batteries, and we have not attempted to recharge them yet.


Nooooooooooooooooooooooooooo, by allowing them to sit without recharging they are likely scrap, if that ever happens again, immediately recharge with a cheap smart electronic charger that regulates amps to a fixed amount or dump charge them for a minute using jumper cables and another charged battery.



claeton said:


> The voltages are the ones measured right after the "industrial accident".
> 
> Any precautions I should take while recharging these SLA batteries the first time after shorting them out?
> 
> Thanks.


NO just keep an eye on them, use a current regulated electronic charger AND DO NOT WAIT TO CHARGE!

Every hour they sit that way they loose more capacity, you SHOULD NEVER ALLOW A BATTERY THAT HAS DROPPED BELOW 11v TO SIT WITHOUT CHARGING OR THEY WILL SELF DESTRUCT AND BECOME COMPLETELY UNUSUABLE IN A COUPLE DAYS!!!!!!!!!!!!

In other words if you would have charged them right away they might still be usuable, now that you have waited more than a few hours they will likely have little usuable capacity.

I would also recommend at this point using a cheap electronic battery charger that regulates the amps to a specific rate, since you did not immediately recharge you will have to charge at 2 amps or so. If you would have gotten to them IMMEDIATELY after the incident I would have recommended hooking them up to a car battery using jumper cables and use your running cars alternator to recharge them part way up to at least a safe level like 11v.

The hard sulphation rate increases by 1000% at voltages below 10.5

Once hard sulphation forms the batteries will not accept charge and can short out.

SO if you have waited more than a few days they may be unusable without a desulphator even then likely at much less capacity.

So in the future; unless you can visually see damage to the case or you check and there is basically 0v be sure to always recharge the batteries right away after such an incident, every hour they sit they become more damaged.

The worst thing that can happen in a well ventlated area is that the battery will blow the circuit breaker on the charger, shorted batteries will not just BLOW up unless left for a long time in the presence of sparks.

So common sense and a watchfull eye will let you know if the batteries are coming up in voltage, if they are sizzling (noise) sparking (noise) arcing, popping or something else you will know they are junk, but unless you charge them you cannot know anything.


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