So I finally finished a project that I've been putting off for a few months.
The goal was to make one of these:
Which Ecotech will sell you for about $165. I considered this to be insane, so I made one myself.
Ecotech's battery is 12V at 18AH which would run my MP10 for 72 hours. I made a battery backup in 30 minutes for less than $20 that will last for up to 30 hours.
If you search online, lots of people rig up lead-acid batteries to a trickle charger, and that works too, but there's a simpler solution out there. Enter the Belkin Battery Backup, which can be had for $17 used off of Amazon. I got mine earlier this year with a brand-new battery. Apparently there's a ton of these on the market and they can be had for pennies. Best thing, they out 12VDC, contain an integrated float charger, and have an audible alarm for when the power goes out or the battery is going bad.
I'd put in a detailed guide, but it's really too easy to make this. Cut the cord from the backup and splice in the correct plug (center pin positive, by the way), and then you're done. I added a 1-amp fuse just in case. Works like a charm. Power goes off, alarm rings, and my MP10 switches to 50% flow at a constant rate until primary power is restored.
Also, If you're looking for a battery backup for your apex...the plug that the belkin backup comes with fits perfectly and outs the correct voltage. So this is an instant apex controller backup for <$20. So buy two.