I have covered LiFePO4 vs. SLA and solar charging for the shack, but neither post answers the question that actually matters for a comms plan: how many days can your gear actually run before you are dark. Here is how to do that math honestly.
Know Your Radio’s Actual Draw, Not Its Rated Draw
A handheld pulling 1.5 amps on transmit and a fraction of that on receive is a completely different power budget than an HF rig pulling 20 amps at full output. The number on the spec sheet is worst case, transmitting continuously at full power, which is not how an actual comms plan uses a radio. Estimate real duty cycle instead, a rough split of receive time versus actual transmit time, since receive current is what your battery mostly sees over a real day of monitoring a channel.
Doing the Math for a Real Scenario
Take the 3-3-3 radio plan as the example, checking in every 3 hours for 3 minutes. That is a tiny actual transmit duty cycle stacked on top of whatever time the radio spends listening in between. A handheld idling in receive most of the day and transmitting for a few minutes at each check-in can realistically run for days on a single battery pack, where the same radio left in a high power scan mode burns through it in hours. The plan itself, not just the battery, is a power decision.
Solar Extends It, It Does Not Solve It
A small panel keeps a comms battery topped off day to day, but it does not turn a marginal power budget into an unlimited one. Cloudy days happen, panels get shaded, and a solar setup sized for your shack’s normal use is not automatically sized for a grid-down scenario where it is now the only input. Budget solar as an extension of your battery reserve, not a replacement for actually knowing how long that reserve lasts on its own.
Build In a Reserve You Never Touch
Whatever runtime the math gives you, treat the last 20 percent as untouchable except for an actual emergency transmission. It is the same logic as never running your car below a quarter tank during hurricane season. A comms plan that runs its battery to zero doing routine check-ins has no capacity left for the one call that actually matters.