Blog · 2026-07-05 · Batteries
The battery decides your robot's weight, runtime, peak power and how carefully you must treat it. Here's how the chemistries actually compare — and a simple rule for matching each one to a build.
Ask "which battery should I use?" in any robotics forum and you'll get four confident, contradictory answers — because each answer is right for a different robot. Battery chemistry is a set of trade-offs between energy per gram, peak current, safety, lifespan and price, and the correct choice falls out of which of those your build cares about most. This guide lays out the trade-offs honestly, chemistry by chemistry, then gives you the matching rules.
Before comparing chemistries, know what you're comparing. Nominal voltage per cell sets how many cells you stack for your system voltage. Energy density (Wh/kg) decides runtime per gram of robot — critical for anything that flies or climbs, merely important for anything that rolls. Discharge capability (C-rating) decides peak current — the difference between a battery that powers four stalling motors and one that sags into a brownout. Cycle life decides cost over time: a cheap pack that dies in 150 cycles is an expensive pack. (If C-ratings and mAh are still fuzzy, read Battery Capacity Explained first — this article assumes those basics.)
Lithium-polymer packs are the default in RC and competitive robotics because they deliver on the two axes that matter there: energy density around 130–200 Wh/kg and colossal discharge rates — even modest packs sustain 20–30C, meaning a 2200 mAh pack can source 40–60 A. Cells are 3.7 V nominal (4.2 V full, ~3.0 V empty), sold as 2S (7.4 V), 3S (11.1 V), 4S (14.8 V) packs, and the flat pouch form factor tucks into tight chassis.
The costs are real. LiPo demands discipline: always charge with a balance charger, never below 3.0 V per cell, never charge a swollen or punctured pack, store at ~3.8 V/cell if unused for weeks. A physically damaged LiPo can vent violently or catch fire — combat robotics rules exist for a reason. Cycle life is the shortest of the lithium family, typically 150–300 cycles before noticeable fade. Treat LiPo as the chemistry you choose when performance justifies care.
Best for: drones, fast rovers, combat robots, anything where grams and amps both matter.
Cylindrical li-ion cells — the 18650s and 21700s inside laptops and EVs — share lithium's high energy density (up to ~250 Wh/kg for quality cells, the best of any hobby option) but package it in a rigid metal can that tolerates handling far better than a pouch. Cycle life runs 300–500+ cycles. The trade-off is discharge rate: standard cells manage only 1–3C continuous, and even "high-drain" cells (Molicel, Samsung 25R class) top out around 15–30 A per cell. Building packs also takes more work: spot-welded nickel strips or quality cell holders, plus a BMS board for protection and balancing — though ready-made packs with BMS built in sidestep all of that.
Best for: long-runtime rovers, telepresence robots, lawn robots, anything that runs for hours at moderate current. Pair high-drain cells with a right-sized motor system and li-ion covers a surprising share of robotics.
Nickel-metal-hydride is the chemistry you can hand to a classroom. Cells are 1.2 V nominal, packs are ubiquitous (the classic 6-cell 7.2 V "battery pack" from RC cars), and the failure modes are benign: over-discharge hurts capacity, not safety; charging is tolerant; a damaged cell just dies quietly. The price is weight — 60–100 Wh/kg, roughly half of lithium — and higher self-discharge unless you buy low-self-discharge (Eneloop-type) cells. Discharge rates around 5–10C are plenty for small robots.
Best for: education, first robots, kids' projects, any build where robustness and safety beat grams. A 7.2 V NiMH pack plus a simple charger remains the least stressful power system in robotics.
SLA batteries are cheap per watt-hour, tolerant, and terribly heavy: 30–40 Wh/kg, and you should only use about 50% of the rated capacity if you want the pack to live. On a mobile robot every one of those extra kilograms circles back into motor torque demand — run the numbers in the Motor Sizing Calculator and watch the requirement climb. SLA earns its place in heavy, slow platforms (big outdoor rovers, robot mowers on a budget) and stationary projects, and nowhere else.
| Chemistry | Cell V | Wh/kg | Discharge | Cycles | Safety effort |
|---|---|---|---|---|---|
| LiPo | 3.7 | 130–200 | Excellent (20C+) | 150–300 | High |
| Li-ion 18650/21700 | 3.6–3.7 | 150–250 | Low–moderate | 300–500+ | Moderate (use BMS) |
| NiMH | 1.2 | 60–100 | Moderate | 300–500 | Low |
| SLA | 2.0 (6/12 V packs) | 30–40 | Moderate | 200–300 @50% DoD | Low |
Figures are typical ranges for hobby-grade parts; individual products vary. Usable capacity also differs by chemistry — the Battery Runtime Calculator applies the correct derating for each.
1. What's your peak current? Sum your motors' stall currents (worst case) or use the peak from your motor sizing. Over ~20 A points strongly to LiPo; under ~10 A opens every option. 2. Runtime or punch? Hours of moderate draw favours li-ion; minutes of high draw favours LiPo. 3. Who handles the battery? Students and shared workshops favour NiMH or BMS-protected li-ion; experienced solo builders can run LiPo safely.
Pick battery voltage to suit your motors, then regulate down for electronics. A 3S LiPo (11.1 V nominal) or 6–8 cell NiMH suits the enormous population of 12 V-class gearmotors; a buck converter derives clean 5 V for the controller. Avoid powering a microcontroller from the same unregulated rail as motors without filtering — motor noise causes the mystery resets that haunt beginner builds. And remember voltage sag: a "12 V" LiPo delivers 12.6 V fresh and ~10 V near empty, so speed and torque fall across the run.
Whatever the chemistry: avoid full discharges (set a low-voltage alarm — they cost almost nothing), avoid charging or storing hot, store lithium at partial charge for long gaps, and retire packs that swell, heat abnormally or lose obvious capacity. Batteries are consumables; good habits just slow the consumption.
Chemistry chosen? Now size it. The Battery Runtime Calculator turns capacity and current draw into honest minutes and tells you the minimum C-rating your pack needs — the two numbers that decide whether your robot performs or browns out.
Chemistry choice comes with an ecosystem. LiPo packs ship with XT60 (up to ~60 A), XT30 (small builds) or Deans connectors, plus a JST-XH balance lead — standardize on one main connector across your packs and chargers, and crimp or solder properly: connector resistance is where peak current goes to die, appearing as voltage sag your calculations didn't predict. Wire gauge matters at robot currents — 16 AWG handles ~10–15 A comfortably, 12–14 AWG for 20 A+ systems — and undersized silicone wire warm to the touch is a warning, not a feature. Finally, put a fuse or resettable breaker on the main lead sized ~1.5× your calculated peak: a short across a 25C LiPo delivers hundreds of amps of consequences, and a ₹50 blade fuse converts that event from fire to inconvenience. NiMH and BMS-protected li-ion are more forgiving here, which is part of their beginner appeal — a good BMS already includes overcurrent cutoff.
Sticker price misleads because chemistries age differently. A ₹1,500 LiPo lasting 200 cycles costs ₹7.5 per run; a ₹2,500 protected li-ion pack lasting 450 cycles costs ₹5.5; a ₹1,200 NiMH pack at 400 cycles costs ₹3. For a robot used weekly the differences are pocket change; for a classroom fleet cycled daily, chemistry choice compounds into real budget. Fold in the accessories each chemistry demands — LiPo's balance charger and charging bag, li-ion's BMS — and the "cheap" option reorders depending on how many packs share the infrastructure. This is also the honest argument for buying quality cells: doubling cycle life at +40% price wins the division every time.
If you remember nothing else: peak current pushes you toward LiPo, runtime pushes you toward li-ion, inexperience pushes you toward NiMH or a BMS-protected pack, and weight-insensitivity is the only door through which lead-acid should enter. Most builds feel the pull of two of these forces at once, and the chemistry that serves the stronger pull — checked against the three questions above — is almost always the right call. When the forces feel balanced, choose the safer, longer-lived option; nobody ever regretted a battery that was merely adequate and boring.