For many years I have used the Sonic Tronics/ McDaniel NI-STARTER and have never been able to run one down in a day of flying unless it was at the end of its life, and that could take years. I carry a single Ni-Starter in my field box or my pocket.
However, for back up, I do have a Northeast Engineering glow plug driver wired to my 12 volt 12 amp-hr field box battery. This not a power panel but a sophisticated true glow plug driver that varies the current to the plug on demand and keeps lit in a flooded engine. I bought one many years ago when I saw it keeping a glow plug brightly glowing under water in a Pyrex baking dish at the Northeast Engineering booth at a WRAM show in White Plains, NY.
The Northeast Engineering glow plug driver is long gone from the market but it appears that the RCATS glow driver does the same thing and has additional features and is portable. For those folks who complain about having to recharge a Ni-Starter, the RCATS may be ideal because its 5200 mAh Li-ion battery may go for months without recharging.
You can watch the RCATS video at
http://www.youtube.com/watch?v=kN8F41o_y4k
It is strange that there are complaints about having to recharge a glow battery but no complaints about having to recharge the transmitter and receiver batteries. Are there any complaints about repeatedly recharging A123 batteries at the field?