In short
Store LiPo packs at partial charge, cool, dry and clear of combustible materials, with any swollen pack quarantined rather than put back on the shelf. Use your charger’s storage mode and the manufacturer’s figure rather than a number from a forum. A LiPo bag limits a small failure; it is not a tested fire enclosure.
Lithium polymer packs follow the same storage principles as any other lithium-ion cell, set out under storing and charging lithium-ion batteries and step by step in how to store lithium batteries. Three things about LiPo are different enough to be worth their own page: the pouch construction, the way the hobby market talks about “LiPo safe” bags, and what to do when a pack swells.
What makes a LiPo pack different
“LiPo” describes the construction rather than a wholly different chemistry. The cell is built as a flat pouch in a soft foil laminate instead of a rigid metal can, which is why these packs can be made thin, light and in awkward shapes — the reason they dominate model aircraft, drones, RC cars and similar equipment.
That construction has two practical consequences for storage.
- Damage is visible. When gas is generated inside a pouch cell, the pouch expands and you can see it. A cylindrical cell in a metal can gives you no such warning. Swelling is the single most useful inspection signal you have, and it is free to look for.
- The packaging is not protection. A foil pouch offers very little against puncture, crushing or a dropped tool. Packs that live loose in a box with propellers, spanners and connectors are being mechanically stressed every time the box moves.
LiPo packs in hobby use are also worked hard: high discharge rates, warm packs coming straight off a flight or a run, and repeated fast charging. None of that changes how to store them, but it does mean the population of packs in a typical model box is more varied in condition than a set of tool batteries, and inspection matters more.
Storage charge and temperature
Partial charge, cool and stable. A cell held at full charge ages faster and holds the maximum energy available to be released if it fails; a cell left to over-discharge suffers internal changes that make later charging genuinely hazardous. The reasoning behind both is set out in storage temperature and voltage.
Most LiPo chargers have a storage mode that takes a pack to the manufacturer’s intended storage level rather than to full. Use it. It is the one piece of automation in this whole subject that removes a human decision, and it means you do not need to trust a figure quoted without a source — the charger and the datasheet agree with each other.
We deliberately do not publish a single voltage or percentage here. The correct figure varies by product, and a number repeated without its origin is not something you can rely on. Two habits matter more than the number:
- Do not leave packs at flight charge. A pack charged for a session and then not used should go to storage charge, not into the box as it is. This is where most stored LiPo sits at the wrong level.
- Check periodically. Packs self-discharge, and one left over a winter can drift into over-discharge. A recurring check — look for swelling, verify the level, return it to storage charge — covers both risks in one task.
What a LiPo bag or box actually does
Fabric LiPo bags and small metal LiPo boxes are sold widely, often described as “fireproof” or “explosion proof”. Those words are marketing, not test results. It is worth being precise about what these products do and do not offer, because the gap between the two is where people get hurt.
What a bag can reasonably do. Keep a small pack physically separated from the combustible material around it, hold sparks and limited flame from a single small cell, and give you a defined place to put a pack you are unsure about. For one or two small packs, a bag on a non-combustible surface away from anything that will catch is a sensible arrangement.
What it does not do. There is no published fire-resistance rating behind the usual bag. It is not tested to EN 14470-1, VDMA 24994 or UL 9540A, and no duration of protection is claimed in a form you could put in an assessment. A pack in thermal runaway vents hot flammable gas under pressure, and a soft bag is not built to contain that — it is built to stop a small event spreading immediately to what is next to it.
A sealed rigid container has the opposite problem. Gas needs somewhere to go, and a closed metal box with no vent path can build pressure. If you use a hard case, it wants to be one designed with venting in mind rather than an airtight box.
As pack count and total energy rise, the case for a tested enclosure strengthens — and it rises faster than the number of packs suggests, because it is energy content that matters rather than pack count. Once you are storing or charging a fleet of packs rather than a handful, the relevant comparison is a cabinet with a tested fire-resistance duration, not a larger bag. See battery cabinets and how to choose one.
When a pack swells
Swelling means gas has been generated inside the cell. The pack has told you something has gone wrong internally, and the decision is already made: it is finished.
- Do not charge it. Not to discharge it safely, not to “see how it goes”, not once more to finish the session.
- Do not puncture or compress it. Deliberately piercing a swollen pouch is advice that circulates in hobby forums and it is a bad idea.
- Separate it now. A defined quarantine spot, away from healthy packs and from anything combustible, and where practicable outside the occupied building.
- Do not put it in general waste. Once a pack is waste it falls under the Waste Batteries and Accumulators Regulations 2009. Use a battery collection point or a licensed collector.
The same applies to any pack that has been crushed, dropped hard, pierced or has been in water, even where it looks fine afterwards and still works.
Charging, which is a separate problem
Storage and charging get conflated because the same box tends to serve both. They are different states: a stored pack is passive, a charging pack is an active process with energy going into it.
Charge on a non-combustible surface, clear of anything that will catch, not on carpet or a sofa and not against a wall of packaging. Keep it off escape routes and away from sleeping accommodation — which is the point that governs LiPo charging in a house as much as at work. Use a balance charger appropriate to the pack, and stay near enough to notice. Where charging happens at volume, a charging cabinet separates the activity from the rest of the building.
At home and at work
Most LiPo packs are stored at home, by hobbyists, and the guidance above is the whole of it: storage charge, cool and dry, clear of combustibles, inspected, swollen packs out.
Where LiPo is stored or charged at a workplace — a model shop, a drone operator, a survey firm, a school technology department — general workplace duties apply, and the arrangement needs to appear in a risk assessment rather than being left to whoever owns the packs. No UK regulation requires a battery cabinet; what the duties require is that you have assessed the risk and can show the controls are proportionate to it. See regulations and how to assess lithium battery risk.
Frequently asked questions
Are LiPo safe bags actually fireproof?
No, and the word is doing a lot of work in the marketing. The usual fabric bag carries no published fire-resistance rating and is not tested to the cabinet standards, so there is no duration of protection to rely on. What a bag can do is keep a small failure separated from the combustible material around it and give you somewhere defined to put a suspect pack. Treat it as separation, not containment.
What charge should LiPo batteries be stored at?
At the storage level the manufacturer specifies, which is partial rather than full. In practice, use your charger’s storage mode — it targets that level without you having to trust a figure from a forum. We do not publish a single number because it varies by product, and a figure without a source is not usable evidence in an assessment. What matters is that packs do not sit at full charge for months and do not drift into over-discharge.
Can I store LiPo batteries in the house?
Yes, with the same arrangements you would use anywhere: storage charge, a cool dry spot, clear of combustible material, and inspected now and then. The placement questions matter more indoors — not on the only staircase or in a hallway that is your escape route, not in a bedroom, not in an unheated shed or a car that swings twenty degrees in a day. A garage or utility area away from the escape route is usually the better option in a house.
What do I do with a swollen LiPo pack?
Stop using it and do not charge it. Move it to a quarantine spot away from other packs and from anything combustible, ideally outside the occupied building, and do not pierce or compress it. Then dispose of it through a battery collection point or a licensed collector — a waste pack falls under the Waste Batteries and Accumulators Regulations 2009 and does not belong in general waste. A swollen pack is not repairable and is not worth the risk of one more session.
Is a metal ammo box a good LiPo store?
It is a common hobby solution and it does address the mechanical side — packs are protected from being crushed or pierced. The problem is that a pack venting inside a sealed metal box produces hot gas with nowhere to go. If you use a rigid case, use one designed with a vent path rather than an airtight seal, and keep it somewhere a failure would not immediately reach anything combustible.