Unbalanced bank question

turbo_wagon

I have a 6x8v 48v bank with 4 new batteries and 2 that are 1 year old. Of course, the new batteries are charging to 10v while the older ones are slightly lower at 9.6v. Is it possible to rebalance the pack or do I need to suck it up and replace the old batteries? (I am kinda cheap, btw) Can I individually charge the old ones up to 10v and expect that they will stay in balance? Is it possible to rejuvenate tired batteries?

I have been following Sergio's thread on the passive voltage regulators and have the components to assemble them but don't understand battery science enough to know whether it will help at all in my situation.

BGW

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NoleFan4Ever

Those are still elevated charges. You have to let them sit at least 12 hours (or 24) to get the true state of charge. If you had 10vdc on all 6 batteries and it was truly putting that out (continuously) you would start having trouble with some of your older electronics.

I would fully charge the pack, wait till the next day, then check each individual battery and the pack voltage. 50.9x is fully charged.

If the batteries are only one (1) year old and maintaining anywhere around 9vdc, I would rock & roll....

And to test "old" batteries for possible rejuvenation, toss them in a tub of water and any that float can be rejuvenated. (The kits are all over the Internet, but I would not waste my money on them.)

scottyb

It is normal to have uneven values when mixing new and older batteries. The new batteries are more capable and responsive. They will charge and discharge faster than the old batteries to the point they over charge waiting for the old ones to come up... but the charger cut off relay sees only the total voltage not the individual voltages. So the new ones get real high and the old ones get a break they don't need, like letting a fat kit sit out a footrace.
This repeats itself until all the batteries are equal and that spells out reduced performance for your new batteries, reduced lifespan too. So if you really are frugal, not just cheap... go buy more new batteries asap.

fsu1tm

WalterM6

I was reading about Lithium Batteries and it said you had to bottom balance all of the batteries for 24 hours before use. This is accomplished by connecting all of the batteries in parallel for 24 hours. This in theory should bring all of the batteries to the same level. It wouldn't hurt to try this with lead acid batteries. Nothing to lose but it might save you the cost of 2 new batteries.

Sergio

What You are describing is just "balancing" not "bottom balancing" and helps getting the Lithium pack initially balanced before the BMS takes over.

turbo_wagon, If You already have the components for the voltage by-pass go ahead and build them.

You will need at least four (one for each new battery), but if You build eight You can double them down on the new batteries.

The older batteries will likely not need them.

The one time charge would not help since the older batteries will discharge faster and charge slower so You need to adjust the charge each time.

Those passive devices will not shunt too much current, but two of them in each new battery may by-pass enough current to help the old ones charge while avoiding damaging the new ones.

If these two older batteries were in the cart for 1 year along side really old batteries, You may not get good results (Damaged vs. Aged).

turbo_wagon

I guess I should have said that this was at elevated charge. I'll skip the tub of water test... doesn't that test also work for witches?

NoleFan4Ever

Htownblue

Thanks to Nole’s Advice, I now have really really clean batteries that are apparently not able to be rejuvenated. It’s ok though, a shady character outside my local batteries plus sold me a packet of Epsom salts, jade shavings, pepper, and armadillo bone dust and said if I put a pinch in each battery cell I’ll get 54V resting voltage on my pack. So thanks Nole, my retrained batteries will now be very clean looking too.

turbo_wagon

After 12 hours all of the batteries measure between 8.6-8.75v.