mterman avatar image
mterman asked

How do I choose what type of battery to use?

Off grid system.
2 x 100/50 MPPT Blue Solar (Plan is to put 4 x 275/300W solar panels on each)

1 x 1500w generic inverter to 230V 24V system.

Main loads are fridge, small stereo system, lights (led bulbs) and sometimes small kitchen appliances (mixer).

Looking to upgrade battery banks. We are looking at a 6 x 220Ah batteries.

The problem is we don't know witch type of batteries to choose, AGM or GEL.
In the future we may get higher power inverter.

Does this system require AGM because of the charging / discharging currents? We are leaning towards the GEL because of longer life. Do the GEL batteries have temperature above witch they shouldn't be charged?

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2 Answers
the-salmon avatar image
the-salmon answered ·


I'm not expert on batteries, so take my advice with a grain of salt, but I'm planning a system similar to yours.

I've been told from a re-seller that the Deka GC15 battery (6V - 230Ah) may be a good choice as well, especially for its quality/price ratio.

It is a flooded lead-acid battery, it should be strong against deep cycles and temperature excursions; on the other hand it has to be stored in a ventilated and dedicated room (not in the living room let's say...).

In my case I was almost convinced to go for Lithium batteries, but the strict temperature range made me change idea.

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mterman avatar image mterman commented ·

Thank you for your answer.

The problem is that we don't have many battery brands or models that we can get our hands-on. The system now runs on Trojan batteries, and when we wanted to upgrade the system we couldn't find more same kind Trojan batteries anywhere to buy ...

We choose to change the brand of the batteries. Our options are limited as I mentioned. We are going with Victron batteries because they are well stocked in the shops, only dilemma left is what kind of batteries to choose.

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the-salmon avatar image the-salmon mterman commented ·

I see.. Trojan batteries should be quite similar to the ones I'm planning to use, are you happy with them? Did they work well?

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mterman avatar image mterman the-salmon commented ·

Trojan batteries seem to be a good value. These are only one year old so I can't testify about longevity. We have 2 x 205Ah AGM Trojan batteries, but that is not enough for our needs so we planned to add 4 more to the bank. But because of tariffs and what not we cannot get any more in eastern Europe so we choose to go with the Victron.

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Tom avatar image
Tom answered ·

Even lead Acid battery have an optimum operating temperature and minimum temperature to charge. They also do catch fire from over charging just ask my buddy. His house just burnt down from charging his golf cart in his attached garage. A sealed battery still produces hydrogen gas and an internal short can make for explosion. At low temp charging the battery resistance greatly increases thus increasing charging time and limiting discharge output.

You need to ask yourself how you intend to use your solar battery system and how fast of a C rating you intend to discharge it.

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the-salmon avatar image the-salmon commented ·

Maybe it is a stupid question: over charging shouldn't happen if the MPPT is working properly, am I right?

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Tom avatar image Tom the-salmon commented ·

You should be fine, but nothing is fail safe because equipment fails. This is why BMS systems are employed. I don't know anyone that uses a BMS on a small lead system because the batteries do not last long and they are low cost.

With my buddies fire when charging his golf cart he was using a proper golf cart battery charger with a programed charge cycle and over charge protection and it failed and burnt his house down.

I am not trying scare you, I am just pointing out lead Acid is not fail safe and you need to use them within specifications. All products have pros and cons.

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the-salmon avatar image the-salmon Tom commented ·

Yes, I agree with you! Thanks

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mterman avatar image mterman commented ·

I'm not specifically worried about the heat of the batteries or overcharging. Of course that is something to worry about in case of the malfunction of equipment.

The subject of my question is the atmospheric temperature, during the summer in the middle of the day air temperature can reach 35 °C.

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Tom avatar image Tom mterman commented ·

That should not be an issue at 35 deg C. 0 deg C and lower will greatly refuse the amp hour output of your Batteries if you do cold weather camping.

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mterman avatar image mterman Tom commented ·

I'm aware of the lower Ah in the lower temperatures, but that is OK because batteries are in the place that is heated during the winter. And our usage is a lover during the winter months.

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