UPS uninterrupted power supply / deep cycle / solar batteries

My guess is there is a thermistor in the inverter circuitry.

 

I had an old UPS "APC 500" that I connected to a car battery, it did work somehow but the output was nowhere what I expected, I think the electronics are designed to a certain level and limited to that...

 

yea that was the first one I tried, it would not even run a 60watt fan, the second unit did, but like I said it did not go the distance, maybe you are right Manzanita? maybe second choice is an inverter or 12v power supply for the laptop and hook up the internet which is luckily 12v to the battery

 

They sell inexpensive Inverters in town, I bought one a while ago, 1000Watts output, thermally sound with fan, can not remember the price but not more than 2000PhP, it's working with a 100AHr. deep cycle battery that's solar charged...
This one will drive my 550Watts electric drill with ease for quite some time...