The "portable" setup is a P.O.S.

The battery barely cranks over larger engines, and the battery dies fairly quickly, usually within the season.
It only holds enough of a charge for an afternoon of flying....

I removed the provided battery and replaced them with two 3800mAh 7.4v rc racing packs...

Now I can turn over 50CC engines ( with the larger starter using this arrangement ) and I can go 2 to 4 full weekends of startups between charges.

I rarely ever worry if I forgot to charge the battery now.

FYI: if you forgo the "portable" pack and simply zip tie the RC race packs in place, as many at our field do... it's about the same price.

It you use smaller packs than I did, say 1900mAh ones ( about $12.00/ea from Nitroplanes which also work ) it's much cheaper yet still provides stronger starts and more duration than the single 1200mAh 12v battery which Tower Sells you.