Your Charger: What Every Number on the Screen Means
Current, voltage, capacity returned, internal resistance, balance and storage mode — every number explained, plus the two settings that destroy packs, the parallel-charging rules, and how to read a pack's health before it strands you.
Updated Jul 22, 2026 · RC Crash Crew
A modern RC charger shows you six or seven numbers and expects you to already know what they mean. Most people learn two of them, guess at the rest, and find out about the others the day a pack fails.
This page goes through every number on a typical charger screen, what it is telling you, and which ones will hurt you if you get them wrong. There is a separate LiPo safety guide on this site covering fires, storage and disposal — read that one too. This page is about operating the charger correctly.
Before anything else: the two settings that destroy packs
Almost every serious charging accident comes from one of two mistakes, and both are made *before* you press start.
1. The wrong chemistry. LiPo, LiHV, Li-ion, LiFe and NiMH all charge to different voltages and by different methods. Charging a LiPo on a NiMH program does not stop where a LiPo needs to stop. Check the chemistry every single time.
2. The wrong cell count. A 3S pack set to charge as 4S will be driven far past its safe voltage. Most decent chargers auto-detect cell count from the balance lead and refuse to proceed on a mismatch — let it, and believe it. If the charger says 3S and you thought it was 4S, stop and find out why before overriding anything.
⚠️ These two are checked *before* every charge, not once when you set the charger up. The pack on the bench is not always the pack you think it is.
The numbers, one at a time
Current (A)
How fast you are pushing energy in. This is the number you set most often.
The 1C rule: charging at 1C means a current in amps equal to the capacity in amp-hours.
- 5000 mAh = 5.0 Ah → 1C = 5.0 A
- 2200 mAh = 2.2 Ah → 1C = 2.2 A
- 6500 mAh = 6.5 Ah → 1C = 6.5 A
At 1C a pack takes roughly an hour from empty. Many modern packs are rated for higher charge rates and say so on the label. The label is the authority, not the rule of thumb — but if the label says nothing, 1C is the safe assumption.
Higher current means faster charging, more heat, and more stress on the cells. Charging fast because you are impatient is a genuine trade against pack life.
Voltage (V)
Total pack voltage, and per-cell voltage on the balance screen. The numbers that matter:
| Chemistry | Nominal per cell | Fully charged per cell | Storage per cell |
|---|---|---|---|
| LiPo | 3.7 V | 4.20 V | ~3.80–3.85 V |
| LiHV | 3.8 V | 4.35 V | ~3.85 V |
| Li-ion | 3.6 V | 4.20 V (varies by cell) | ~3.7–3.8 V |
| LiFe / LiFePO4 | 3.3 V | 3.60 V | ~3.3 V |
| NiMH | 1.2 V | ~1.4–1.5 V under charge | n/a |
A LiPo charged on an LiHV program goes to 4.35 V per cell. That is well past where a standard LiPo should ever be, and it damages the pack whether or not anything dramatic happens on the day.
Capacity returned (mAh)
How much went in during this charge. This is one of the most useful numbers on the charger and almost nobody watches it.
Compare it to the pack's rated capacity. If a 5000 mAh pack that you ran to a sensible cut-off only takes 3200 mAh, that pack has lost capacity. Track it over time and you can see a pack aging long before it fails.
It is also a safety check: if a pack takes more than its rated capacity, something is wrong — a bad cell, a charger fault, or a pack that was already damaged. Stop.
Internal resistance (IR / mΩ)
How much the pack resists current flowing. Lower is better — less energy wasted as heat, more punch under load.
The critical thing about IR: use it for comparison, not as an absolute. Readings vary by charger, by temperature, by capacity and by state of charge. A number that means "healthy" on one charger means something else on another.
What to actually do with it:
- Compare the cells within a pack. They should be broadly similar. One cell reading noticeably higher than its siblings — say a third higher or more — is a cell going bad, and it will get worse.
- Compare the pack to itself over time. Log it. Rising IR is the clearest early warning of a pack on the way out.
- Compare packs of the same type. A pack much higher than its identical twin is the tired one.
A pack with one high-IR cell is the one that puffs. Finding it early is the whole point of this number.
Balance
Lithium packs are made of individual cells in series, and cells drift apart over time. Balance charging monitors every cell through the balance lead and bleeds off the ones that get ahead, so they all finish together.
- Always balance charge lithium packs. "Fast charge" without the balance lead is a habit that ends with one cell being taken past 4.2 V while the pack total looks fine.
- Plug the balance lead in every time. It takes two seconds.
- A pack that will not balance — one cell always lagging — is telling you that cell is failing.
The modes on the dial
Charge — charges without cell-by-cell balancing. Faster. Not what you want for lithium in normal use.
Balance charge — charges and equalizes the cells. This is the default for every lithium pack.
Storage — brings the pack *to* about 3.80–3.85 V per cell, charging or discharging as needed. This is the mode that most extends pack life, and the one most people never press.
Discharge — runs the pack down at a set current. Useful for NiMH conditioning; mostly unnecessary for lithium.
Cycle — repeated charge/discharge. Genuinely useful for waking up and measuring NiMH packs. Pointless and harmful for lithium.
Storage charge is the habit worth building
A lithium pack sitting at full charge degrades measurably faster than one sitting at storage voltage. It also sits closer to the state where a fault becomes a fire.
The rule: if the pack will not be used in the next day or two, put it to storage voltage.
That is it. That single habit does more for the life of your packs than any charger you can buy. A pack left fully charged for months may come back puffed, high-IR, or simply unable to hold its capacity — and none of that is recoverable.
Equally, do not leave a pack sitting empty. A fully discharged lithium pack left for weeks can drop below the voltage where it is safe to recharge at all. Storage voltage is the middle, and the middle is where they keep.
NiMH is a different animal
NiMH does not have a voltage you charge *to*. The charger detects when the pack is full by watching for a tiny voltage drop at the end of charge — this is delta-peak detection.
- The peak sensitivity setting (in millivolts per cell) is how twitchy that detection is. Too sensitive and the charger stops early; not sensitive enough and it overcharges.
- NiMH tolerates being trickle-topped in a way lithium absolutely does not.
- A hot NiMH pack at the end of charge is normal. A hot lithium pack at the end of charge is not.
- NiMH self-discharges significantly while sitting. A pack charged last month is not charged now. Low-self-discharge (LSD) cells are far better at this.
Parallel charging — real risk, real rules
Charging several packs at once from one channel using a parallel board. It works, it is common, and it removes several of the safety margins you normally have.
The rules are not optional:
- Identical cell counts. Never mix a 3S and a 4S on the same board. This is the one that starts fires.
- Similar voltages before connecting. Packs at very different states of charge will dump current into each other the instant they are joined — through the thin balance wires, which are not built for it. Get them within about 0.1 V per cell of each other first.
- Similar capacity and condition. A tired pack alongside healthy ones will be pushed harder than it should be.
- Set the current for the total. Four 5000 mAh packs in parallel is 20,000 mAh — 1C is 20 A, and your charger and its power supply must actually be capable of that.
- Connect the main leads before the balance leads, and disconnect in the reverse order.
If any of that feels like too much to hold in your head at the end of a long day, charge them one at a time. That is a completely reasonable choice.
Your power supply is part of the charger
A charger's advertised output is what it can do if it is fed enough. A "200 W" charger running from a small 60 W supply will simply throttle back, and you will spend a long time wondering why a big charger is charging slowly.
Watts = volts × amps. Work out what you actually need at the output, add headroom for losses, and size the supply for that. Many chargers display input voltage — if it sags noticeably when charging starts, the supply is the limit.
Where and how to charge
Covered properly in the LiPo safety guide, but the short version belongs on any page about chargers:
- On a hard, non-flammable surface. Not carpet, not the sofa, not a wooden workbench with a cloth on it.
- In a charging bag or metal container, with nothing flammable nearby.
- Never unattended, and never overnight while you sleep.
- Never charge a pack that is puffed, damaged, has been in a crash, or is still hot from a run. Let it cool to room temperature first.
- Never charge a pack below its safe minimum voltage — a lithium cell that has been run flat and left is not something to revive.
- Know in advance what you would do if one started venting. Deciding at the time is too late.
Reading a pack's health from the charger
Everything above adds up to a routine that tells you when a pack is dying, weeks before it strands you:
- Capacity returned, compared to rated and to last month.
- Cell IR, compared cell-to-cell and over time.
- Balance behavior — does one cell always lag?
- How warm the pack gets during a normal charge.
- Physical check — any swelling at all means retire it.
Any one of those drifting is worth watching. Two of them drifting together means that pack has done its work, and the right answer is to retire it properly rather than to find out the hard way.