Typical 12v Lead/Acid battery (above) used in many commercial bait boats. Weighing in at a massive 2.2Kg!!
These are my units (above). Charger is a Vector NX85 and the battery packs are rated 5000mah.
Prices vary but expect to pay £15 to £25 for a 5000mah pack and around £10 if you want to drop down to 2000mah (which will cut your running time down by 60%).
The Charger is available brand new on Ebay for around £25 and well worth the investment. Also as an added bonus you can hook up the charger to your car meaning you can still recharge your bait boat without needing a mains socket!
Batteries & Charging
When choosing power for your boat you'll need to consider a number of things
Voltage
As I had already invested in some good quality batteries from as early as my 'toy boat', I simply felt that I would stick with what I already had which is 7.2v....a lucky choice as it turns out.
Looking at commercially available bait boats, most use 12v but some use 7.2v. From my perspective, I wanted to build a small and lightweight boat and therefore didn't want very heavy batteries. The standard sealed lead/acid 12v batteries used for baitboats such as Viper and Waverunner weigh a massive 2.2Kgs (more than my whole boat including batteries). From a design perspective this means that the boat is now going to displace 2.2ltrs of extra lake water...and push an extra few pounds through the lake....not for me.
Technology
If you're sticking with 7.2v you'll then need to consider which technology you're going to use. There are two readily available:
LiPo - Lithium Polymer Batteries
NiMH - Nickel–Metal Hydride Batteries
LiPo is the more modern of the technologies and is significantly more expensive. If you end up choosing LiPo you need to special chargers and possibly LiPo compatible ESC's. The main difference between the two types when in use is that LiPo's discharge their power at a constant rate. What I mean by that is that they will deliver 7.2v until suddenly going virtually flat. With NiMH the drop off in voltage is more gradual. LiPo's are used by people into racing model cars where you want maximum power for the whole race. As an angler I don't need this and don't want my boat to go dead in the water when I least expect it. With NiMH I get an indication of how much charge is left in my battery by how fast my boat travels...I can then guage when I need to change the power pack.
mAh Rating
You'll find this on all 7.2v battery packs. Milliamp Hour (mAh) is important because it's the easiest way to distinguish the strength or capacity of a battery. The higher the mAh, the longer the battery will last. Batteries with different mAh ratings are interchangeable. Think of a car petrol tank. Voltage is how much petrol is being used, and mAh is the size of the tank. The bigger the tank (mAh) rating the longer the device will run. I use 5000mAh rated battery packs and they will happily cope with a full day fishing
Chargers
There are plenty of very cheap chargers out there. But be careful with this area. Every charger is rated for how much power is can put into the battery pack over a 1 hour period and this is expressed either in mAh (Milliamps per hour) or Amps (1000mah = 1.0a). If you have a 5000mAa battery pack and your charger delivers 500mAh (0.5a) then it's going to take 10 hours to fully charge. I was fortunate to find a second hand charger on ebay which can deliver up to 5.0a per hour. This means I can recharge a pack in 1 hour.