Battery Management

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FRC robots rely on a single 12 volt, 18 AmpHr, sealed VRLA (valve-regulated lead-acid) battery for power. Battery Management is critical for the team's success, because:

  • Nothing can ruin your day faster and more certainly than a robot failing in competition due to battery failure (plus this is a real rookie failure). Such failure may be either due to poor battery performance, connector failure or poor management processes.
  • Batteries are a significant investment to our team, costing about $45 each.

The team currently maintains about 12 competition batteries. The team purchases about 3 new batteries per year (plus one from the Kit of Parts) to replace those removed from service due to performance.

Since late 2011, the team has marked batteries, started testing them and keeping records. Earlier batteries still in service at the time were included in this identification system.

Battery Safety

First, batteries are heavy. Dropping them will damage almost anything they land on. Like toes. Needless to say, always wear closed-toes when handing batteries. Dropping batteries will also damage the batteries.

Never short the battery terminals.

The battery electrolyte is sulfuric acid (H2SO4). Sulfuric acid causes rapid chemical burns. Normally, the sulfuric acid is safely contained by the battery case, but if this case is damaged (such as by dropping), the acid may be released. In case of acid spill, neutralize any spilled acid using baking soda (Sodium Bicarbonate - NaHCO3) before cleaning up the spills. Wear chemical-resistant (not cloth or leather) gloves while working with acid spills. Baking soda and appropriate gloves are stored in the robot cart.

Never use batteries having damaged cases or popped valves. Remove these from service immediately and recycle.

Never pick up batteries by the cables.

Object lesson - the great Oscar Way Battery Crash

Replacing 4 or so batteries per year is not such a burden.

But on 10-August-2013, as we were moving out of Oscar Way and to the CCIU, we lost nine (9) competition batteries in an instant as they fell from a cart and landed on concrete. Fortunately no-one was hurt.

Battery Technology

Lead-acid batteries are the oldest type of rechargeable battery. They've got poor charge density (both Amp*Hr per mass and per volume), but provide high surge current (making them ideal for automotive batteries where starters require high current), have long service life and low cost vis-à-vis alternative rechargeable technologies.

In lead-acid batteries, the positive electrode is lead oxide (PbO2(s)) and the negative electrode is lead (Pb(s)). The electrolyte is aqueous sulfuric acid (H2SO4(aq)). This represents the fully-charged state. As the battery discharges, both positive and negative electrodes are converted to lead sulfate (PbSO4(s)). two electrons are released for every lead atom converted to lead sulfate. As the battery discharges, the sulfuric acid concentration in the electrolyte drops. Charging reverses this reaction.

Our 12 Volt batteries comprise six (6) cells in series.

Valve-regulated lead-acid (VRLA) batteries are sealed and also immobilize the electrolyte via either a gel (Gel Batteries) or by absorbing the electrolyte into a glass fiber mat (AGM - absorbed glass mat). AGM batteries are certainly used by FRC (and maybe Gel batteries as well).

VRLA batteries may be used in any orientation.

Battery Management Policy

In general
Battery - top view
  • Batteries are identified with a 1 or 2 letter code. Batteries entering service up to the start of 2014 are lettered A-Z. Subsequent batteries enter service with 2-letter identifiers: AA-AZ; then BA-BZ; ZZ (should we live that long).
  • Batteries identify the team (1640) and the year in which the battery entered service.
  • Pick up batteries by the battery case; not by the cables or connector
  • Handle batteries carefully; do not drop
  • Competition-rated batteries are indicated by a blue sticker.
  • Non-competition batteries are indicated by a yellow sticker.
  • Failed batteries are indicated by a red sticker and leads are removed.
  • Failed batteries are recycled at the earliest possible convenience.
  • Batteries are Competition (blue sticker) rated if:
  1. They have been CBA tested and delivered >11.0 AmpHr during their latest CBA test; and
  2. They rate "Good" by Battery Beak and >100% charge after being fully recharged; and
    Battery - front view
  3. Have not been identified during an ongoing competition as a "problem-battery"; and
  4. Have not been dropped since the last CBA test; and
  5. Have no visible signs of damage to the battery case, relief valve, cables or connectors.
  • Batteries are non-competition (yellow sticker) rated if:
  1. Their latest CBA test yielded capacity of 7-11 AmpHr; or
  2. They rate "Fair" by Battery Beak and >100% charge after being fully recharged; and
  3. Have not been identified during an ongoing competition as a "problem-battery"; and
  4. Have not been dropped since the last CBA test; and
  5. Have no visible signs of damage to the battery case, relief valve, cables or connectors.
  • Batteries are unrated and may not be used in competition if:
  1. They have not been CBA tested within the past 9 months; or
    Connector with plug inserted
  1. They have been dropped since their last CBA test and have no visible damage to the case; or
  2. Have been identified during an ongoing competition as a "problem-battery".
  • Batteries having damaged cables or connectors must have these repaired or replaced prior to use. CBA testing is not required to return a battery with repaired cables or connector to service.
  • A battery is failed and must be permanently removed from service, cables removed and battery recycled if:
  1. The battery case is visibly damaged in any way; or
  2. The relief valve has opened; or
  3. Any leakage or liquid or gel is observed (CAUTION - CORROSIVE! - use battery clean-up kit); or
  4. The battery becomes hot to the touch while charging; or
  5. The CBA indicates <7 AmpHr; or
  6. The Battery Beak indicates "Bad" or <100% charge immediately after charging the battery.

At competition

  • Change the battery prior to each match after preparing the robot for the coming match.
  • Remove old battery for recharging. If removed in-pit, place battery on charger immediately. Otherwise charge the battery when returning to the pit. Never re-insert white plastic plug into the connector of a used battery.
  • Test each new battery with a Battery Beak prior to installing in the robot or placing on the robot cart. Battery Beak must indicate that the Battery is "Good" and >100% charged. Verify that battery has a blue sticker.
  • When installing a new battery in the robot, the pit crew does not remove the white plastic plug and does not connect the battery to the robot's power connector.
  • Handle all batteries carefully by the battery case (not by cables or connectors)
  • Observe condition of cables and connectors - repair or remove from service pending repair any battery with damaged cable or connector.
  • After removing a battery from the charger, immediately insert the white plastic plug into the connector and place the battery into the "Charged" queue.

CBA Testing

  • CBA testing of ALL competition should be conducted no more than two weeks prior to:
  1. The team's first Qualifying Event of each season; and
  2. The District Championship (presuming we qualify); and
  3. The FRC Championship (presuming we qualify); and
  4. IRI (presuming we participate)
  • CBA testing is encouraged prior to all competitions.
  • CBA testing should be at 7.5 amps load; 10.5 volts terminal voltage.

Battery Testing

In spite of the fact that we test all batteries with a Battery Beak (Manufactured by Cross the Road Electronics - marketed by AndyMark) before competition, we experienced two battery failure in competition: one at Westtown (battery AD) and a more complete one at MAR Championship (battery AF) where we just managed to crawl to the batter at the start of the match.

As a result, we tested all competition-rated batteries 18-20 April using the CBA (Computerized Battery Analyzer) III (manufactured by Optim Engineering - marketed and sold by West Mountain Radio). The CBA measures the voltage of a battery over time under a fixed current load until a set terminal voltage is reached. For this testing, the load is set to 7.5 amps; terminal voltage to 10.5 volts. The CBA reports Amp Hrs.

Battery test 160418.jpg
The data collected on the batteries is here (right):

And the CBA III performance charts (below):

CBA III graph.jpg

Three batteries were removed from service as a result of the testing: AD, AE & AF. Note that AC had previously been removed from service. The batteries AC-AF all entered service in 2014 and came from two consecutive orders of two batteries each. With the exception of these four batteries, the only other gap in our in-service batteries is "V" from 2013. "U" is the oldest battery in service (also from 2013), so "V" almost certainly died of old age. This makes the AC-AF group appear as if it may be associated with a manufacturing QC lapse.

Read the full CBA III Report.

Our last full battery test with the CBA III was conducted in March 2014. These test are labor and time intensive. Since then, we have relied on the Battery Beak to assess battery health.

Key findings of this test are:

  1. The Battery Beak does not identify all failed batteries. As a result, reliance on the Battery Beak alone exposes the team to battery failures in competition (as at Westtown & MAR Championships).
  2. The CBA III does appear to correctly identify failed batteries (as identified by competition failures) which the Battery Beak misses.
  3. The CBA III appears to also identify failing batteries (such as "AE"), allowing these to be removed from competition service prior to obvious failure.
  4. It is clear that the team should reinstitute a regular CBA testing regime.

The CBA III is no longer manufactured. The team has ordered a CBA IV from West Mountain Radio. This augments rather than replaces the old CBA III (with is compatible with Windows 10). The team has also ordered two replacement batteries to be delivered to our pit at FRC Championship.