Same as above. Tried several and had so-so results. I managed to waterproof the battery, but didn't like having to turn the vest on before zipping up the drysuit, especially on those days when it was HOT on the surface and cold on the bottom. And there was no way to change the heat setting once in the water,
I went with the Golem Gear vest. About $1,000 but find I don't want to dive without it. Even on cave dives, when I've got an hour or two on deco, the heat is great. You turn it on when you need it and, with the GG, you have 3 different heat settings to crank it up as it gets colder. Probably could have paid for it with all of the other vests I tried and discarded.
I second the recomendation for Golem Gear. I've dove mine for a year now and love it. It controls easily from the switch on the battery. The low setting is plenty even in the 38 degree water we dive. It's alot easier to turn a switch than to plug in a cord with drysuit gloves.