Using a mix of Lead Acid Low Maintenance and Maintenance free battery

[ipogram]

Hi!

I am planning to setup a 240W solar system, with 30A PWM charge controller, to use around 400Wh capacity at night. It is very light and use for 'lighting' only, which is around 70watts per hour peak.

I am planning to use old truck batteries for my 4pcs battery bank:
- old means 2yrs
- since we replace truck batteries every 2 yrs, planning to use them 1-2yrs more. and this will be the cycle of replacement.
- truck batteries usually comes in a pair
- planning to mix 2pcs 12V65AH low maintenance lead acid and 2pcs 12V50AH maintenance free batteries, (in SERIES).

Is is OK to mix up these batteries and use them for 1-2yrs max? as sing 2yr old batteries will cost me $0 and will have faster ROI.

Thanks!

[SeanB]

If they are free then use them. They will have a shorter life already, but in a solar application they will be fine as long as you do not discharge them too much each night. Just check that they do not actually have a set of refilling caps under the label, as many are easy to open to check the water level and to top up with distilled water if needed. In this application they might give 5 years of service.

[ipogram]

Hi SeanB,

Ok great! Some more quick questions:

1. How about mixing 2pcs 12V100Ah low maintenance battery with 2pcs 12V50Ah maintenance-free, in series? Is it still OK? I mean in terms of difference in capacity by almost 50%.

2. if you are given 4pcs maintenance-free and 4pcs low maintenance free batteries, all are 12V50Ah capacity, which will you use in your battery bank? - I've heard low maintenance has greater capacity and output but needs to be checked every 2-4weeks. Any inputs?

Thanks!

[SeanB]

If you are using in series try to match capacity in each string. Thus if you have 2 100Ah units use them in series. You can mix different capacity ones in parallel, but in series you need a match. Thus a string of 2 100Ah in series, in parallel with another string of 2 50Ah in series. Mixing low maintenance and regular just means you will have one set die first, likely the low maintenance ones, though check that you can add water to the supposedly sealed ones as they often are the same battery.

[ipogram]

Hi SeanB,

Ok. great! Thanks for your inputs!