| Electronics > Beginners |
| Mixing old and new lead acid batteries in parallel |
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| e100:
Are there any disadvantages or issues if you put a new lead acid battery in parallel with an 8 year old lead acid battery? The goal is to have more Ah at the same voltage. I'll be individually charging them to the same voltage then putting them in parallel with a temporary resistor in between them to limit the current. Once equalised I'll just treat them as one large battery. |
| paulca:
I believe the old battery will not hold it's peak voltage and will pull the new one down with it. So you will lose effective capacity on the new battery. My main solar battery when brand new would hold 13.1V for 24 hours after charge. Now, about 300 50% cycles in it drops to 12.9V within a few hours. You could test both your batteries, by boost charging them for an hour, then floating them for a few hours and finally leaving them overnight to see how they hold their voltage. |
| e100:
--- Quote from: paulca on May 09, 2019, 08:56:57 am ---I believe the old battery will not hold it's peak voltage and will pull the new one down with it. So you will lose effective capacity on the new battery. --- End quote --- So the new battery will be trickle charging the old battery, or is it more complex than that? |
| digsys:
--- Quote from: e100 --- So the new battery will be trickle charging the old battery, or is it more complex than that? --- End quote --- Unknown, depends on the relative chemical states of the 2 batteries etc etc BUT, there will be some actual loss. Why not wear a 0.4V loss (Shottky diodes), or 0.6V loss (STandard diodes) - putting them on the OP of each battery. The "newer / better" one will do most the work for a while, until the "weaker / older" one catches up. Need more details on what you want to do - how they are wired, as there may be other choices. |
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