If you're using an ego-t, might want to consider the ego booster. i just bought one the other day and haven't received it yet, so i can't personally vouch for it. but it will turn your regular ego battery into a variable voltage PV. instead of the 3.4v, you can get up to 4.7v. you can probably get some mods cheaper, but when you factor in the cost of extra batteries, chargers for those batteries, etc, it may equal out to be the same considering you already have all that with your ego-t. if you want reviews, go to youtube and search for ego booster. it's out there, it's an idea, others will have others ideas which may be better.