Mini-Project: A Battery Management & Logging System

An unhealthy battery is both a performance problem (brownouts mid-match) and a safety problem (a swollen or shorted SLA cell can vent or arc). This mini-project turns a pile of anonymous bricks into a tracked fleet.

Step 1 - Number and label every battery. FRC uses a single 12V 18Ah sealed lead-acid (SLA) battery such as the MK ES17-12 (AndyMark am-0844, sold as a set of two). Write a permanent ID (B1, B2, ...) and the purchase date on each with a paint pen. Never carry a battery by its cable - WPILib explicitly says do NOT carry a battery by the cables, because it fatigues the internal lugs and tabs and raises resistance.

Step 2 - Establish a baseline with the Battery Beak. The Battery Beak (am-0995, also sold by CTR Electronics) mates directly to the Anderson SB-50A connector and applies up to an 18A load to report state of charge, open-circuit voltage, voltage under load, and internal resistance. Healthy targets per WPILib: internal resistance below 0.015 Ohm (the manufacturer spec for most batteries is ~0.011 Ohm); a fully charged battery reads 12.7-13.5V open-circuit.

Step 3 - Build the log. Create a shared spreadsheet with columns: Battery ID | Date | OCV (V) | Internal Resistance (Ohm) | State of Charge (%) | Cycles | Notes. Test every battery at least weekly during build and before every match. Example rows:

B1 | 2026-02-14 | 13.1 | 0.012 | 100 | 22 | baseline good
B4 | 2026-02-14 | 12.9 | 0.021 | 95  | 61 | resistance high - RETIRE

Step 4 - Apply hard retirement rules. Retire a battery if ANY of these is true:

• Internal resistance climbs above 0.020 Ohm (WPILib's stop-using-for-competition threshold).
• It reads 12.5V or lower while sitting on an idle robot (swap and charge before a match).
• Any sign of bulging, swelling, melting, leaking, or a burned terminal - quarantine it in a sturdy plastic bin and recycle.
• It has been dropped or mechanically stressed (treat as suspect and re-test thoroughly). Most FRC batteries lose their competitive edge after a few seasons of heavy use; track cycles so age never sneaks up on you.

Step 5 - Charging discipline. Use a smart charger (am-4968_1 single-bank, am-4968_3 three-bank, or am-5539_4 four-bank) that modulates current to the battery's needs. WPILib says to wait for a battery to cool before recharging - the case should not be warm to the touch, and fifteen minutes is usually plenty. Store batteries charged to extend life. A periodic full-capacity test with a battery analyzer confirms each battery still delivers at least its rated capacity (WPILib notes a healthy battery should still have ~11.5 Ah) before you trust it in eliminations.

The finished artifact - labeled batteries plus a live log with explicit retirement criteria - is exactly the kind of evidence a UL Safety Advisor and award judges reward.