"How long does it last" means two different things: hours of power from one charge, and years before the battery wears down. The first is arithmetic you can do from watt-hours and watts. The second is only partly answerable, because seller pages list charge cycles, not years. Both are covered below with the seller's figures.
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Two questions in one
Per charge is the time a full battery runs your device. It depends on the battery's watt-hours (Wh) and the watts your load draws.
Over the years is how many times the battery can be charged and used before it holds noticeably less. Seller pages answer that in cycles, and sometimes attach a condition such as "to 80% capacity". Neither My Patriot Supply product page printed a number of years of life when read on 2026-11-04, so this guide does not state one. What follows is the formula for the first question and example arithmetic for the second.
Runtime per charge: the formula
Runtime in hours equals watt-hours multiplied by 0.85, divided by the load in watts.
The 0.85 is our own planning assumption for conversion losses, not a seller figure. Leave it out and you get an ideal ceiling (Wh divided by watts). Real units rarely hit the ceiling, so we show the planning figure and call it an estimate.
Worked example for the Grid Doctor 300, which the seller lists at 320Wh, with a 40W load: 320 x 0.85 = 272Wh usable, and 272 divided by 40 gives 6.8 hours. The ideal ceiling is 320 divided by 40, which is 8.0 hours. My Patriot Supply's page says the 300 runs a CPAP for up to 8 hours, which matches the ideal ceiling for a 40W load. The 40W is our example load, not a measured CPAP figure; read your own machine's label.
The table uses the example loads from our data file. These watt figures are labelled assumptions, not sourced facts, and motors start with a surge above their running watts.
| Example load (assumed watts) | Grid Doctor 3300, 2,048Wh | Grid Doctor 300, 320Wh |
|---|---|---|
| Wi-Fi router (10W) | 174.1 h | 27.2 h |
| LED lights, 4 bulbs (40W) | 43.5 h | 6.8 h |
| CPAP, no humidifier (40W) | 43.5 h | 6.8 h |
| 42-inch LED TV (80W) | 21.8 h | 3.4 h |
| Mini refrigerator (80W) | 21.8 h | 3.4 h |
| Full-size refrigerator, average running draw (150W) | 11.6 h | 1.8 h |
| Gas furnace blower (400W) | 4.4 h | 0.7 h, over the unit's 300W output |
| Sump pump, running (800W) | 2.2 h | 0.3 h, over the unit's 300W output |
Estimates for 2026-11-04 prices and specs, planning efficiency 0.85. The 300 is rated for 300W continuous, so the last two rows exceed what it can deliver, whatever the hours say. Add loads together before dividing: a router plus lights plus a CPAP at the assumed watts is 90W.
Read the Grid Doctor 3300 review and the Grid Doctor 300 review for the seller's spec tables behind these numbers.
Cycles to years: example arithmetic
A cycle is one full discharge and recharge by energy. Dividing the seller's cycle figures by how often you would run them gives an example span. These are labelled arithmetic, not predictions:
| Cycles | One full cycle a day | One full cycle a week |
|---|---|---|
| 800 (the 300's figure to 80% capacity) | 2.2 years | 15.4 years |
| 2,000 (the 300's "2,000+" figure) | 5.5 years | 38.5 years |
| 3,500 (the 3300, and the 300's second figure) | 9.6 years | 67.3 years |
The seller's page says 2,000+ cycles (with 800 cycles to 80% capacity) in the 300's specifications and 3,500 cycles in its technology blurb. This guide prints both and does not choose. The 3300's page prints 3,500.
Treat the spans as limits set by the cells only. Weekly-use numbers run past any promise the seller makes, and the pages list no calendar life, so they are best read as "cycles are unlikely to be your limit". A unit used for outages a few times a year spends very few cycles. How you store it matters at least as much, and the chemistry is covered in LiFePO4 portable power stations.
Storage and temperature care
My Patriot Supply's page says the unit should be stored at 60% charge or more, recharged every three months, and kept away from heat above 113 F. The listed operating range is 14 to 104 F, and charging is listed at 32 to 104 F. Treat those as the rules that go with the cycle figures. A unit stored empty in a hot garage works against any cycle rating, whatever the number printed on the page.
A practical routine for a backup unit:
- Put a three-month reminder on a calendar to top it up.
- Store it indoors at room temperature where you can reach it.
- Check the charge level before a forecast storm.
- Use only the cables the seller's manual approves.
- Read the user manual, as the seller's page directs.
Does an EMP feature change how long it lasts?
No claim on the seller's pages links the 3300's EMP feature to battery life. My Patriot Supply says the 3300 has built-in EMP Intercept Technology, designed to help protect internal components; this site found no independent test of that claim, which the EMP claims guide covers in full.
Which unit lasts longer?
Per charge, the 3300 holds 6.4 times the capacity of the 300 for 6.0 times the price (a gap of $2,500: $2,997 against $497, read 2026-11-04), so it runs the same load roughly 6.4 times longer. Over the years, the seller's cycle figures put the 3300 at 3,500, and the 300 at either 2,000+ or 3,500 depending on which line of its page you read. Which unit suits you depends on loads; see the 3300 vs 300 comparison. For the overall decision, start from the best portable power station for home backup.
FAQ
How many hours will a power station run my device?
Multiply the unit's watt-hours by 0.85 and divide by the device's watts, then treat the answer as an estimate. The ideal ceiling skips the 0.85.
How many years will a power station last?
The seller pages read here list cycles, not years, so this guide gives no figure. Dividing cycles by how often you use them gives example spans, shown above.
Does leaving it plugged in or stored full hurt it?
The seller's page says to store the unit at 60% charge or more and recharge every three months. It does not say more than that on the point, so follow the manual that comes with your unit.
Sources
- My Patriot Supply, Grid Doctor 3300 product page, read 2026-11-04: https://www.mypatriotsupply.com/products/grid-doctor-3300-emp-solar-generator
- My Patriot Supply, Grid Doctor 300 product page, read 2026-11-04: https://www.mypatriotsupply.com/products/solar-generator-300w-by-grid-doctor
- U.S. Department of Energy, Appliances and Electronics (energy equals watts times hours), read 2026-11-04
Update history
| Date | Change |
|---|---|
| 2026-11-04 | First published |