For everyday use I have a McDaniel R/C / Sonictronics metered ni-starter. When I'm flying fairly often it'll go a month or so without recharging. My field box has a 12v gel cell and a power panel also, but my real backup battery is a plastic battery box for 4 d-cells from Radio Shack, rewired to put the circuit in parallel instead of series. I made a cardboard box cover to keep it nice and clean. With 4 Energizer D cells you can hook it up to a new Fox 35 on the test stand and crank on it till it finally fires and it's not discharged. I put it together about 2 years ago and it's still going strong. If it dies a recharge is as close as the nearest grocery, drug store, super store, the emergency flashlight in the backseat, etc. It also lights up a glow plug as bright as the sun. The only downside is the weight.