So in the previous post I detailed all the improvements I'm dong with the sump pump system. We have had rain bad enough to overwhelm the main pump, so even with a generator I wanted a backup. I was looking for a battery backup that would: - have as much or more capacity than a 1/3hp AC pump - have at least an 8hr run time so if we lost power while at work I dont have to rush home to start the generator - Recharge in a less than a day - Be able to run on AC or DC so it can also kick in to help the AC pump or if the AC pump fails - not cost thousands of $ I looked at a lot of options, including homebrewing my own system with a boat bilge pump and a big battery. In the end I settled on the Basement Watchdog Big dog system as it would do everything a homebrew would but cost less. And it has all kinds of automated failure monitoring options (batery, pump, etc test) built in. Verdict - It works very well, and has good capacity. But there is one major flaw. They use a flooded deep cycle ( i think its aobut 140Ah) and their built in charging controller is just a dumb bulk charger. The battery is always powering the system and they monitor it and when it drops to 12.3 VDC under load it gets a 20amp top off charge. They rate te pump for AC operation because the pump load is 12 amps so the charger can feed it and still keep the battery full. I can see why many users complain the batteries only last 2-3 years. Since they are only occasionally bulk charging the battery is often sitting in a partial discharge, and never gets a good equalization - so the batteries are probably sulfating. If they just spend the couple extra bucks and add a real 3 stage charger (bulk->absorption->float) and keep the battery on a 13v trickle all the time they would probably get 7-10 years life. I had a conversation with their tech support who tried to tell me that only maintenance free batteries need 3 stage charging so either they dont have a clue or are happy to sell more batteries. Anyway, I will be disconnecting the battery once every couple months for an equalization charge on a good 12v charge controller. Anybody out there who has one of these systems I suggest you do the same. IF I were to do it all again I would homebrew instead and setup a DC bilge pump (Rule, etc), with a big Group 4 or group 8 AGM battery and a GOOD lead acid charge control/power supply like the kind that off grid folks use (Something from Iota Engineering or Powermax for example). All of this might cost close to a grand and lack all the alarms, etc but would last a lot longer and probably more reliable.