My friend bought an expensive car starter “jumper box” from Costco when it was on sale, but when he went to use it about 3 months later the battery in the jumper box was dead and wouldn’t charge no matter how long he left the box plugged into a 110v outlet.  He brought the unit to me thinking I could fix it but the battery was shot and was going to cost $75 + shipping to get a drop in replacement 12v sealed lead acid battery for the unit.  He told me to just junk it for parts. 

After thinking about it for a month or so I thought maybe I could modify it to hold a larger 12v lawn mower battery.  I knew it would work just fine if I could find a battery that fit.  I took it apart again to take some internal measurements then headed for Wal-Mart.  Sure enough I found a nice riding lawn mower battery that would fit if I cut out the front-side of the jumper box housing.  The battery even had nice through-hole terminal connectors for bolting on the cables.   This mod ran about $35 for the replacement battery and a 2 foot threaded rod with some lock nuts to hold the battery in the unit.

What follows are some bad (sorry) videos of the modification and some photos.  Its possible any dead jumper box could be brought back to life this way because I would think most take the same size internal 12v sealed lead acid battery and its not a lot of work.

This is a photo of the original 12v sealed lead acid battery still in the unit.  Tip: (photos are much faster than writing down wiring diagrams before disassembling).

I left it charging for 2 days on a 2amp 12v car charger and this is all the voltage I could get on the unit (1.93v).

This is a photo of the replacement EverStart lawn mower battery I got at Wal-Mart. Its just the right width but it’s to large front to back to fit in the jumper box housing.  If  you try this mod make sure the + and – are on the correct side because this battery comes both ways.

I drilled a hole in each corner of the front-side lower panel.

Say hello to my little friend “Air Saw”  }:-)

This opening is just big enough for the EverStart battery to slide into place.

Perfect fit!. As you will see in the final video I added a bent over threaded rod run through the sides to hold the battery from tipping out or jostling about.

Video of the final product.