I have an Exide invamaster 1500imst short tubeler normal battery of 12 volt, 150AH, C10. Now I want to connect this battery with a solar battery of 12 volt, 150AH, C20. Can I connect this normal 12 Volt 150AH C10 battery with a solar 12 volt 150AH C20 battery in series for my 24Volt solar system. Will it damage the battery or what will be happened if I use them in series for a solar inverter of 24 volt battery system with 1200 watt solar pannel.


Can you - yes. Is it a good idea - no.

A 150AH @ C10 and 150AH @ C20 battery are not the same "size" because one is rated at the 10-hour discharge rate and the other is rated at the 20 hour discharge rate.

Since you have not specified some other chemistry, I'm assuming both are lead-acid 12V batteries, as the majority of 12V batteries are.

If by "normal" you mean "automobile starting" battery, that one may have short life due to construction optimized for a very different service than a deep cycle (or "solar") battery. On the other hand, by pairing them you are limited to the solar battery's discharge rate if you want to get rated capacity (150AH @ 20hr - 7.5 A - at 24V about 180 Watts before inverter losses, perhaps 150 Watts after inverter losses.)

If that seems like a very low power output, welcome to the ugly realities of solar power, where almost everyone starting out undersizes their battery bank until they have the expensive lesson that it costs a lot to be cheap.

  • Hopefully not the people around here that we educate! – Harper - Reinstate Monica Oct 19 '20 at 15:45
  • Oh the disaster stories I've seen here in sunny Florida. – JACK Oct 19 '20 at 16:15

You're not only mixing different models. You're also mixing new and used batteries. This means, as a pack, you will get the performance of the worst battery. When it gives up the ghost, you will be left with 1 battery that still has some useful life, and you will be tempted to pair it with a new battery. Don't. At that point replace with all new.

Keep in mind...

The problem with lead-acid as a solar battery is that they give very short life. They give a lot shorter life when they are deep cycled.

Now you think "Full use of the battery's range from 100% to 0% is the entire point of a battery, that is its most basic function. Surely Harper, you can't be saying a lead-acid battery can't do that!"

Yeah, that's exactly what I'm saying.

And that's not entirely unheard of in the battery business; even with lithium (though it's not nearly as bad). Tesla locks out (in software) the bottom 20% of the battery's range, which greatly increase the service life of the battery.

With lead-acid, it is much worse. You should research this yourself, but many wise solar designers say the bottom 70% of nameplate capacity is unusuable. Do not draw more than 30% of capacity from a lead-acid on a daily basis - that is, don't plan to dip it below 70% charged. If you have 150AH @ 24V, plan to use 45AH @ 24V.

It's OK to dip it to say 50% or 40% SOC on an occasional basis, but don't make a habit of that, or it'll significantly shorten the life of your pack. Dipping it all the way down to 10% SOC, your battery will be toast in 20-100 deep cycles. And that's assuming it's built as a deep-cycle battery; a car starting battery will fare worse.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.