Lead-acid chemistries prefer light cycling and full recharge between those cycles. Lead-acid batteries are traditional cycled to 50% depth of discharge because it offers a balance between duty life (years between failure) and bank size.¹⁾ Pulling the bank below 50% DoD in emergnecies will not automatically cause damage assuming a full charge is accomplished ASAP.

This article is about the intentional and chronic depletion of lead-acid banks below the 50% mark, followed by vigorous recharging. This might be desirable when:

• reducing the weight impact of lead banks
• one wants to make use of old/damaged batteries whose capacity has declined

For folks willing to trade battery longevity for some amount of increased capacity, common low-end targets for low voltage disconnect are:

• 60% DoD / 40% SoC, ~12.0 rested volts
• 75% DoD / 25% SoC, ~11.7 rested volts
• 80% DoD / 20% SoC, ~11.6 rested volts

Deep cycling generally extends the amount of time for a battery to complete Absorption.

• get power back into the battery ASAP after deep discharge; drive for alternator charging or run a generator to get bulk stage going. Solar alone might be sufficient but it might require meaningful overpaneling.

While you may not be able to increase the actual Absorption duration,²⁾ you can achieve a similar effect with one or more of these techniques:

• if duration setpoint is maxxed then set Vfloat == Vabs. Absorption duration will effectively be “until the sun goes down”.
• charge at a lower current (charging minimum). While overall charging will take about the same amount of time, Bulk's share of that time will increase and Absorption will take somewhat less time.
• charge at a higher voltage (Vabs), this will decrease Absorption duration. Keep a close watch on water levels for flooded batts, and also mind the max allowable voltage for AGM/Gel.