Batteries, Chargers, and More

Battery Myth | Will a Small Charger Maintain a Large Bank of Batteries?

Quick answer: No.

When you are dealing with a bank of batteries that is collectively larger than a car battery (max 100 amp/hours), you should crunch the numbers to find the ideal charger for your situation. Normal, static power drain on a brand new battery can be as high as 2-3% a month, which in the case of a 1000 amp battery pack (total) would translate to roughly 30 amps.

Assuming the batteries are hooked up to something, it would be fair to double that. If your batteries are not new, the drain will likely be even more. So triple that number. If we assume a total 10% monthly drain, in this case 100 amps, you can see that you are tasking a small battery charger to recharge the same amount of power normally reserved for a larger charger.

Battery Tender Plus 12 volt 1.25 Amp 3 Stage Smart Charger BT-021-0128If we use a Battery Tender Plus as an example (1.25 amps output), you can see that it would need to run at full capacity for 80 hours per month simply to maintain that 1000 amp battery pack. Any small trickle charger (anything under 5 amps) would have to work at full capacity for quite a period of time.

If a small trickle charger is being used at full capacity for too many hours it can either time out, in which case it will shut down automatically, or simply burn itself out.

NOCO Genius GEN1 12V 10A On-Board Battery ChargerWe recommend that you should size a maintenance charger to be no smaller than about 1.5% of your battery packs full rated value. For this scenario, the Genius 10 Amp Charger will work well to simply maintain the charge. But the Dual Pro 12 Volt 15 Amp Charger will meet the 1.5% minimum just fine. If you need to replace charge that has been drained by use, we recommend you go as close to 10-20% of the full value as possible. Our Iota 90 Amp Charger would be the smallest charger we suggest for a battery pack this large.

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