Ecogen battery draining problem,

Yes it can.... Some (many, all, ?) backup gensets are designed expecting to be connected to utility power and use it to keep the genset battery charged.

If you have problems with the battery over charging, you can replace the battery charger with a different (better) AC to DC battery charger. Or if you don't have AC mains (off grid)l, you can use a solar panel + small (good quality) solar battery charger to keep the battery up.

What size and type (Amp*Hour, Voltage, flooded cell, AGM, GEL, etc.) does your genset use?

-Bill

Running 5% to 13% is typical for solar--A 5% rate of charge is OK for something that is not cycled daily... 1% to 2% rate of charge will keep up with the float/self discharge of the battery--But will do real well at recharging the battery after the genset cranks (and if the genset does not have a 12 VDC alternator to recharge the battery during run-time).

• 80 AH * 14.2 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 74 Watt panel/array

You probably should measure the battery discharge current (no 120 VAC charging)--Use a DC Current Clamp DMM (like this one from Sears).

You may have unknown but "significant" discharge current (running genset logic)--So need to make sure the battery and solar array are "sized" appropriately to support both the battery charge rate and the (possible) "vampire" loads of the genset systems.

Just like designing for any off grid system loads needing battery bank/solar array sizing.

-Bill