Depending on your budget, and how seriously you take your preparedness, I'd suggest a rechargeable such as the Surefire 8AX for routine patrol use (110 lumens for 50 mins), and a smaller lithium powered light with uprated lamp for instant maximum brightness backup (I'd suggest 9P/ C3 with P91 200 lumen lamp, runs for 20 mins with high output lamp).
I'm a military aircraft engineer, and I use my 8AX everyday, and even more at night. The B90 Ni-Cd sticks can be picked up cheap, and take a couple of hours to charge. 8AX is about 7 inches long, and fits well into many belt pouches. As a backup when I'm on active duty, I have a choice between my M3 (225 lumen), Z3 (200 lumen), 9P (200 lumen), or C2 (65 lumen).
There are other chioces of rechargeable light, and it's possible to run many of the Surefire range on aftermarket Pila rechargeables, but the 8AX kit (light, charger (mains AND 12 volt) and 2 batteries) is an off the shelf option with a lifetime warranty and proven record.