RadiO
Lantern batteries are not rechargeable, and $18 is a lot of money for a rather wimpy non-rechargable battery.
Below is a link to the Radio Shack lantern battery data sheet. It is rated at 7.5 AH, however it has a very high internal resistance of 2 ohms, and the greatest current draw shown on the data sheet is only 2 amps. If you short it out, you can only get I=V/R=12/2=6 amps out of it in a 1 second pulse (a measly 72 watts). That enough to fire 1or 2 Estes ignitors but probably not a copperhead. (If you only want to fire Estes ignitors, 4 AA Alkalines in series delivering 6 volts work just fine.) This battery will not last very long as a launch battery, and once it's dead, you have to throw it out. It can't be recharged.
https://data.energizer.com/datasheets/library/primary/carbon_zinc/industrial/732.pdf
As Micromister said, 12 volt lead acid gell cells used of emergency lighting and computer UPS applications are inexpensive and rechargeable.
Below is a typical 7 AH Gell Cell data sheet that you can purchase for $18-$25 at a good electronics supply store or from a number of on-lines sources.
https://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_VRLA_LC-R127R2P.pdf
The internal resistance of the battery is listed as 0.040 ohms, so it can theoretically deliver I=V/R=12/0.040=300 amps on a dead short (for a short time anyway). This is much more appropriate for firing ignitors. With the potential of delivering 300 amps, (3.6 KW) it's not a toy, so you won't find one in your local department store.
Note that the gell cell actually has a curve at 23 amp current drain, and it will actually deliver that current for 8 minutes. If you look at a typical copperhead igintor, it will typical ignitor consumes 0.005 AH of the battery capacity (~20 amps for ~1 Second), so you could expect ~700 firings from this battery before you have to recharge it, however it will last a lot longer if you trickle charge it for a day or so after each use.
Any automotive trickle charger will top off the battery. Well maintained and stored around 70 F, the battery will last about 5 years. If you charge it and disconnect the charger, it will last even longer.
Bob Krech
