I run a shifter and had a similar question. I called up the AIM folks and they told me just grab a 9.6V RC battery. Here is what I purchased from Amazon for $16 bucks:
<h1 id=”title” class=”a-size-large a-spacing-none” style=”box-sizing: border-box; padding: 0px; font-family: Arial, sans-serif; text-rendering: optimizelegibility; font-weight: normal; font-size: 21px !important; line-height: 1.3 !important; margin: 0px 0px 0px !important 0px;”><span id=”productTitle” class=”a-size-large” style=”box-sizing: border-box; text-rendering: optimizelegibility; line-height: 1.3 !important;”>Tenergy 9.6V 2000mAh NiMH High Capacity Battery Pack for RC </span></h1>
I bought a charger as well. I mounted it right in front of my gas tank, and I charge it in place.
Hope this helps,