1. Charging circuit

Charge current: I=0,45V/R2
Power-dissipation by R2: (0,45 * 0,45 / R2) !
Please adjust 13,8V by R5 without connected battery.

D1 - D4, D6 :

charge-current less than 1A: 1N4001 (up to 1N4007)
charge-current up to 2A: 1N5401

D5:  1N4184 , 1N4001.

Transformer: 15 V max 2 A

The L200 must be cooled.

2. Simple charging circuit

based to the PB137.

Charging-Current: 1,5A.