One day off grid on two batteries
Two power banks, a 60 watt panel, a satellite terminal, a laptop and a phone. We did the arithmetic before designing the bag, and the answer was not the one we wanted.
BY FIELD // LAB / / 4 MIN READ
The question.
Can two airline legal power banks and a 60 watt folding panel run a Starlink Mini, a MacBook Air and a phone for a working day, with no mains power anywhere?
This matters to us because the Relay Bay, the Command Pack and the Nexus Organizer are all sized around that kit. If the answer is no, we are designing a bag for a setup that does not work.
So we did the arithmetic first. This is a planning model using manufacturer figures, derived estimates and explicit assumptions. Nothing here has been measured on our kit.
What you actually get out of a battery.
A 27,650 mAh Anker Prime is rated 99.54 Wh, which is deliberate: 100 Wh is the ceiling you can carry onto an aircraft without airline approval. Two of them is 199 Wh on paper.
You do not get 199 Wh. Conversion from the cells to USB-C, and from USB-C into a device battery, costs you. Anker publishes the figure themselves without framing it as a loss: one bank charges a 13 inch MacBook Air about 1.28 times. That laptop battery is 52.6 Wh, so 1.28 charges is 67 Wh delivered out of 99.54 Wh stored.
That is 68 percent, and it is 68 percent for charging a laptop. It is not a number you can spend twice. The terminal is a direct load that never charges an internal battery, so it does not pay that second loss, and treating it as though it does is how you end up counting the same loss at both ends of the sum. Everything below stays on the storage side, where the batteries actually live, and each loss lands once.
The budget, and the thing that eats it.
Starlink publishes 25 to 40 watts average for the Mini. We take 30, which sits inside that range but under its real midpoint of 32.5, so read it as the optimistic end rather than the safe one. Ten hours of that is 300 Wh.
The computer and the phone are almost noise by comparison. A full MacBook Air recharge is 52.6 Wh into the battery, about 78 Wh drawn from a bank once you account for the delivery loss. A phone is around 14 Wh into the battery, about 21 Wh drawn.
| Load | Into the device | Drawn from storage | Share |
|---|---|---|---|
| Satellite terminal, 30 W for 10 h | 300 Wh | 333 Wh | 77% |
| Laptop, one full recharge | 52.6 Wh | 78 Wh | 18% |
| Phone, one full recharge | 13.9 Wh | 21 Wh | 5% |
| Total | 432 Wh |
The answer is no, and by how much.
Two full banks hold 199 Wh. A 60 watt panel does not make 60 watts: manual aiming, heat and angle mean 55 to 70 percent of nameplate across perhaps four or five usable hours, so call a good day 195 Wh at the panel and a poor one 132 Wh. Getting that into a bank costs you again. Take 90 percent and you are putting 176 Wh or 119 Wh into storage. Every one of those numbers is an assumption, and the harvest is the softest of them.
That is 375 Wh in storage on a good day and 318 Wh on a poor one, against 432 Wh of demand. You are 57 Wh short, or 114 Wh short. Feed the laptop and the phone first, as you would, and the 99 Wh that costs leaves about eight hours of terminal on the good day and closer to six and a half on the bad one. Neither figure is a runtime in real weather.
So the honest answer to a ten hour day with the terminal always on is no. Not by a catastrophic margin, but no.
Which changes the design, not the kit.
The interesting part is not the shortfall, it is the distribution. The terminal is three quarters of the budget on its own. Everything you would instinctively worry about, the laptop and the phone, is the other quarter combined.
A third bank buys about three hours of terminal, and costs you the weight, the bulk and a carry-on argument. Scheduling the link costs nothing. Four hours of terminal needs 133 Wh, or 232 Wh once the laptop and phone are in, which leaves 143 Wh spare on a good day and 86 Wh on a poor one. Run those same four hours with no sun at all and two banks still come up 33 Wh short.
That is why the Relay Bay is a bay you set down and deploy rather than a pocket you walk around with. You open it when you need the link. A terminal that is convenient to leave running is a terminal that flattens your batteries by mid afternoon.
What we have not proved.
None of this has been measured. It is arithmetic on published figures, and published figures are optimistic in ways that are hard to see. The 30 watt terminal load is an assumption within the published range, not a measured average or its midpoint. The solar harvest is the most variable number here by a wide margin and the one most likely to be worse than we have assumed.
The 68 percent delivery efficiency is derived from a marketing claim about charging a specific laptop, not from a bench measurement, and it will differ by cable, by charger and by state of charge. It also cannot be applied to everything equally, which is a judgement rather than a measurement: a laptop battery loses energy twice, once in the bank and again charging its own cells, while the terminal is a direct load that only pays the first. We have taken that first loss at 90 percent. If it is worse, and it may be, the shortfall grows.
We will publish the measured version when there is a sample to measure it with. Until then, treat this as the reason the bag is shaped the way it is, not as a performance claim.
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