Hey there thanks for the response, well I cannot really lower my power much more, nonetheless 300W should be unusual (peak). I figured since there is a DC/DC converter I'm not really pulling those amps from the auxiliary battery, but from the main battery (58V), that is IF the DC/DC (58V->12V) can supply that kind of power. It takes a month or so of light-use to discharge the auxiliary battery, which means I'm drawing some power (most of it actually) from the DC/DC. If the specs of the DC/DC converter were available I would be able to tell, if I'm discharging my batteries because of insufficient charge (more power amps draw from the 12V line than supply by the DC/DC) or is it just the problem everyone else is having but aggravated because of my load (old charger not being able to keep the auxiliary battery in good health).
A second battery could certainly work , but I think it would only solve the second hypothesis above, because if the DC/DC that charge the auxiliary battery/batteries cannot supply power to charge a battery and provide me the 150-300W, then a second battery won't either, it would just take more time to discharge. Another possibility I've been thinking is to install a DC/DC converter from the 58V traction battery to 12V with enough power, this would probably solve issues regarding "drawing too much amps from the 12V", but if the issue is in the charger, then I think the 12V auxiliary battery would eventually discharge, just slower.