Choosing the Right Battery
In an R/C glider or sailplane, battery choice affects more than just how long the radio stays on or how many motor climbs you can make. Battery type changes the aircraft's all-up weight, nose balance, launch performance, climb rate, and even how convenient the model is to live with between flying sessions.
Some battery types are heavier but forgiving and easy to charge. Others are much lighter and store more energy for their size, but require greater care during charging and storage. In practice, most sailplane pilots end up choosing among four chemistries: Ni-MH, Li-Ion, Li-Po, and LiFePO4.
This page compares all four with glider use in mind, especially where weight versus capacity, charging convenience, and overall suitability matter most.
Why Battery Choice Matters in Sailplanes
Powered sport models can often tolerate carrying extra battery weight if the motor is strong enough. Sailplanes are different. In a thermal ship, handlaunch glider, slope model with onboard pack, or electric sailplane, unnecessary battery weight usually hurts performance. The heavier the aircraft becomes, the faster it tends to fly, the more sink rate increases, and the less willing it may be to float in weak lift.
That said, lighter is not always automatically better. Many gliders need weight in the nose anyway to achieve the correct center of gravity. In those cases, a somewhat heavier battery may do double duty by providing both usable capacity and needed ballast. So the ideal battery is often the one that gives you the capacity you need at a weight that helps the airplane balance correctly without adding dead lead.
Nickel Metal Hydride (Ni-MH)
Ni-MH packs were once the standard receiver battery in many sailplanes, replacing Nickel Cadmium (Ni-Cd) cells, and they still make sense in many installations. They are generally made from cylindrical cells and are easy to recognize by their simple two-wire output lead. Almost always the same connector is used both to power the plane and to recharge the pack. Ni-Cd battery packs were the only type of rechargeable batteries in the 70's and 80's as the newer battery chemistry of Nickel Metal Hydride hadn't been available for modelers use.
Weight vs. Capacity
Ni-MH has the lowest energy density of the four battery types on this page. That means it tends to be the heaviest option for a given capacity. A Ni-MH pack that offers enough duration for a day of flying will usually weigh more than an equivalent lithium-based pack.
In a sailplane, this extra mass can be a disadvantage if the airplane is already nose-heavy. But in some models, particularly older gliders or aircraft needing nose ballast, that added weight may actually be useful.
The other thing to note about Ni-MH batteries is that you can now get them in very high capacity so the weight difference between these and Lithium chemistry is less and less. I still like using Ni-MH batteries for my combat gliders as they're so safe to use and charge over and over.
Benefits and Charging Convenience
Ni-MH is valued for simplicity. It is comparatively forgiving, does not require cell balancing, and can often be charged with very basic chargers. For many pilots, especially those with older equipment, this convenience is a major advantage.
The tradeoff is that Ni-MH self-discharges more than lithium packs, roughly 2% per day. And this voltage tends to sag more under load, and the pack is bulky for the energy it stores. However you can find many, many different configurations of these multi-cell packs. Packs in standard 2x2, 1x4, 1x4 + 1 (5 cells), etc. are available thru many battery supply companies and in addition, some can make custom packs to your desired configuration as well.
Best suited for: older receiver-only installations, simple glider radio systems, and pilots who value ruggedness and straightforward charging over minimum weight.
Lithium Ion (Li-Ion)
Li-Ion packs used in model aircraft are commonly built from cylindrical cells such as 18650 types. They offer substantially better energy density than Ni-MH and are attractive when long duration matters more than extremely high discharge current. Most Li-Ion batteries labeled "Li-Ion" are actually Lithium Cobalt Oxide (LiCoO2) in chemistry.
Weight vs. Capacity
Li-Ion packs provide excellent capacity for their weight. Compared with Ni-MH, they can deliver much longer run time at a lower overall mass. This makes them very attractive for sailplanes carrying several servos, flight electronics, or telemetry for long periods.
They are usually not quite as light or as high-current capable as Li-Po packs in equivalent sizes, but for many glider applications their balance of weight and capacity is excellent.
Benefits and Charging Convenience
Li-Ion offers long duration, low self-discharge, and physically sturdy cell construction. It is often a very good choice for receiver power or for systems where current demand is moderate and endurance matters.
Charging is more involved than Ni-MH because the pack must be charged with a lithium-compatible charger. Some packs include a separate charge lead or balance connector, depending on how the pack is assembled.
Best suited for: receiver and avionics packs in larger sailplanes, endurance-focused setups, and aircraft where every gram matters but extreme motor current is not required.
Lithium Polymer (Li-Po)
Li-Po packs are the most common batteries used in electric-powered model aircraft. In sailplanes, they are especially popular in electric-launch models because they combine low weight with excellent discharge capability. They are usually identifiable by a main power connector plus a separate balance lead used during charging.
Weight vs. Capacity
Li-Po packs offer very high energy density and are usually the lightest practical way to carry a substantial amount of energy onboard. They are also able to deliver high current for a motor climb without excessive voltage drop.
For electric sailplanes, this makes Li-Po the default choice in many power systems. The pack can be kept relatively light while still supplying strong climb performance.
Benefits and Charging Convenience
The main advantage of Li-Po is performance. These packs are compact, light, and capable of very high discharge rates. For motorized gliders, that usually means better climb capability for a given battery weight.
The downside is that Li-Po charging requires more care. A proper balance charger is strongly recommended, over-discharge should be avoided, and the pack should be handled carefully during charging, storage, and transport. Convenience is lower than Ni-MH, but performance is usually much better.
Best suited for: electric sailplane motor packs, high-performance launch systems, and installations where low weight and high current are both critical.
Lithium Iron Phosphate (LiFePO4 / Li-Fe)
LiFePO4, often shortened to Li-Fe, has become a favorite for onboard receiver and servo power because it combines many of the benefits of lithium chemistry with an excellent reputation for safety and long service life. Like Li-Po, these packs usually have both a main power connector and a separate charge or balance lead.
Weight vs. Capacity
Li-Fe usually falls between Ni-MH and Li-Po in energy density. It is lighter than Ni-MH for comparable usable capacity, though usually not as light as Li-Po. In practice, that makes it a very appealing compromise in sailplanes that need dependable onboard power but do not require the absolute highest energy density.
Its nominal cell voltage is lower than Li-Po, which can be an advantage in some receiver and servo installations.
Benefits and Charging Convenience
Li-Fe is known for a stable chemistry, long cycle life, and a lower fire risk than Li-Po. Many pilots consider it one of the most confidence-inspiring battery types for valuable sailplanes carrying expensive radio gear.
Charging still requires the correct charger setting for LiFePO4 chemistry, but the packs are generally considered less fussy than Li-Po in day-to-day use.
Best suited for: receiver and servo systems in larger gliders, pilots who want a strong safety margin, and installations where reliability is valued over squeezing out the very last bit of weight savings.
Comparing the Four Types
| Battery Type | Weight for Capacity | Discharge Ability | Charging Convenience | Main Advantages | Main Drawbacks |
|---|---|---|---|---|---|
| Ni-MH | Heaviest of the four | Moderate | Very convenient, simple chargers often work | Forgiving, rugged, easy to use | Bulky, lower energy density, self-discharge |
| Li-Ion | Very good | Moderate | Needs lithium-compatible charging | Excellent duration, efficient use of weight | Lower current capability than Li-Po |
| Li-Po | Excellent | Very high | Requires careful balancing and handling | Lightweight, compact, ideal for motor loads | More sensitive during charging and storage |
| Li-Fe | Good | High for many onboard uses | Needs correct LiFe charge mode | Safe, long-lived, stable chemistry | Slightly heavier than Li-Po for similar capacity |
Connector and Charging Notes
The diagram above also shows a useful practical distinction between these battery types: how the aircraft gets power from the pack and how the pack is charged.
Connector types also vary from one battery to another. The important point is not just the shape of the connector, but whether the pack uses a single combined power/charge lead or separate discharge and balancing leads.
Which Battery Should You Use?
For a simple older glider with just a receiver and a few servos, a Ni-MH pack may still be entirely reasonable, especially if the model benefits from the extra nose weight. For a larger sailplane where long duration and lower weight matter, Li-Ion is often an excellent choice. For electric-launch models where motor current is high, Li-Po remains the most common and most practical solution. And for pilots who want an onboard pack with a very strong reputation for stability and long life, Li-Fe is one of the best all-around choices.
In the end, the right answer depends on the airplane, the current draw, the desired flight duration, the center of gravity, and how much charging complexity you are willing to accept. In sailplanes, battery selection is always a balancing act between weight, capacity, performance, and convenience.