5 things that help you keep your phone charged in a blackout

The mAh number on the box is measured under lab conditions that have nothing to do with reality. Heat losses, voltage conversion from the bank's 3.7V cells to the 5V USB output, and the phone's own charging circuitry together eat roughly 20–30% of usable capacity. Add a worn cable that isn't rated for fast charging and you lose more. Most people discover this on day two, when they expected a full top-up and got 60%. Running the real number before the outage means you know whether you have three days of emergency comms or one — not a nasty surprise at 2am.

Car USB ports are wired to the 12V accessory circuit. When the engine is off, drawing current to charge a phone pulls directly from your starter battery. A phone pulling 10–15W for two hours can drop a standard car battery 5–10% of its reserve — manageable once, but a compounding problem over several days. More importantly, if temperatures are low and the battery is already marginal, you risk not being able to start the car when you actually need to leave. Running the engine for 20–30 minutes while you charge costs almost no fuel relative to the protection it provides; your alternator will restore what the phone took in the first five minutes.

When the grid goes down, a phone that can see one bar of signal but cannot hold a connection is working harder than a phone with no signal at all — the radio keeps ramping up power trying to grab a partial connection. During a storm, damaged cell infrastructure means your phone may spend the entire night hunting for service it cannot find. That alone can drain a full battery in six to eight hours. Aeroplane mode kills all radio functions in one tap, dropping idle drain to almost nothing. Most people do not need overnight comms during a power cut; they need a charged phone in the morning. This is the single cheapest way to extend your reserves.

A standard power bank tops out at around 26,800 mAh (roughly 100Wh) because of airline carry-on regulations — most products cluster just below that ceiling by design. A portable power station (Jackery, EcoFlow, Bluetti and similar) sits above it, typically at 300–500Wh in a unit roughly the size of a shoebox. At 300Wh you can charge a modern smartphone around 25 times, run a CPAP machine overnight, and power a small lamp — which shifts the outage from genuinely stressful to merely inconvenient. These units cost £200–£350, run on lithium batteries, produce no fumes, and are designed for indoor use. The overkill tier — 2kWh+ home backup systems — costs five to ten times more and is almost never worth it for renters or most households. For anything involving a powered medical device, check with your provider about specific power requirements and contact your electricity supplier about priority service registers.

A power bank runs out. A power bank paired with a solar panel is a loop. A 25W foldable panel in direct summer sun delivers roughly 10–15Wh per hour of genuine sunlight — enough to meaningfully top up a bank during the day without fully recovering it from zero. That does not need to be the goal: if you are also using aeroplane mode overnight and charging intelligently, keeping a bank at 40–70% through daily solar input is achievable in most summer outage scenarios. The honest caveat is that in British winters, heavy cloud, or north-facing flats, output can drop to a quarter of the rated figure. Worth knowing before you rely on it.