How to maintain standby batteries?

[Alex]

Hi, some advice needed please. I have a RCT-AXPERT 3K inverter hooked up to two OmniPower AGM 180Ah 12V batteries in series. I only use the inverter as a back-up solution where I manually have to go turn on the unit in case of power failure. Now the question is should I leave the inverter connect to the AC to float the batteries 24/7 or can I turn off the inverter for a week or two and then float the batteries for a few hours every now & then to keep them topped up? How often should I run a cycle (20-50% DOD) to keep them healthy?

 

Datasheet for OmniPower AGM OPS180-12:

Constant Voltage Charge (25'C)

Cycle: 14.4-14.9V (Initial current 36A)

Standby: 13.6-13.8V

 

Do this translate to 28.8V bulk charge for two in series & 27.2V float? Then lastly my inverter allows two charge settings 20A or 30A which would be better? 

 

Thanks.

[Guest]

My 2 cents. Yes, keep the inverter connected. It is not good to have batteries stand for long periods of time with no charge.

Also good idea to use them a few times, that the juices move a round a bit.

 

10% of battery amp hour is a good thumb suck for charging, so 2 x 180ah (I presume 24v) is 180ah = 20amps charge setting.

[___]

A good battery charger will drop to maintenance mode after 24 hours of float charge, and then it will alternate between float and maintenance. I know on the Victron's you can enable or disable this feature. SO on a 24V bank, what it will do is float them at 27.6 (or whatever you set it to, but that's the usual value) and then after 24 hours it will drop to 26.4. And then every day it will take them up to 27.6 for a few minutes.

 

The point of going down to maintenance mode is to avoid boiling away too much electrolyte and shortening battery life. Because a battery held at 27.6 (which is higher than it's natural equilibrium) will continue to gas out small amounts.