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The SLA charger kit is discontinued. The supply of circuit boards has been exhausted, and after careful consideration, the cost of producing more boards vs. current demand does not justify the expense.

I am leaving the documentation available to the community. Thanks to all who purchased the charger, I trust it will continue to meet your needs.

Lead-acid cells are a reliable power source for operating radios and supporting equipment. Characteristics of the lead-acid family of cells include prolonged standby capability, high capacity, and high current discharge capability. A key factor in obtaining optimum performance from this battery technology is a proper charging environment. Charge voltage and current must be accurately controlled and matched to battery temperature to obtain maximum energy return and long life. This charger uses a charge controller IC designed to accomplish this.The charge controller provides three charge states:

Bulk charge
The charger operates in a high-current bulk charge mode for most of the charge cycle.
When the voltage reaches a programmed threshold, the charger switches to overcharge mode to complete the battery. Charging continues at the programmed bulk charge rate until the charger enters the float charge state.
Float charge
When the voltage reaches the upper programmed limit, the charger enters the float charge mode. The voltage is reduced slightly below the upper limit, causing the charge current to taper off, but the full bulk charge current is available. The battery may be left on the charger in the float mode indefinitely without damage.

A fourth state protects the battery, the charger, and the pass transistor if power is applied and the battery is severely discharged, has a shorted cell, or is connected with reverse polarity. Current is limited to 1/10th the maximum charge current until the voltage rises to a minimum safe threshold. The charger switches to the bulk charge mode to begin a full charge cycle when the minimum threshold voltage is reached.