The protection circuit is not a big project and the parts can be purchased for $12. I no longer have steady enough hands to do a neat job.
Enclosure 3*2*1 Radio shack 270-1801 $3.19
100K resistor Radioshack 271-1347 $1.49
Protection circuit board www-all-battery.com 32071 $6.97
Connector
(You need to Login or Register to view media files and links) 015000045 $1.72- $1.45
2 6-32 X1/2” brass screws ??
GLUE Marine Goop ??
(You need to Login or Register to view media files and links) (You need to Login or Register to view media files and links) Like this only do not put the 2 output screws on the same side of the box. If pliers are dropped on this one they could short out the unit or if in a aluminum canoe they could both touch the side at the same time. And do it neater!
This setup is only suitable for light loads of less than 1 amp because of the small leads. The card max continuous current is 4 amps.
Charging
Car battery charger set to trickle charge and with about 2 ohms in series with the charger. Charge through the protection board using the same connections as the load.
2 .91 ohm 10 Watt RadioShack 10WD91 resistors $1.21 each $2.42
I did not have a suitable resistor so I used about 8 inches of some Nickel-Titanium single strand wire I had for a different project. That is some strange stuff makes a good resistor but hard to make good electrical connection to.
Puckster
A set of 9 Energizer Ultrimate Lithium will supply 250ma at > 11 volts for 12 hours. They can be purchased at Sams Club for about $17/set.