When a Slinger Bag tennis ball machine battery stops charging or begins losing runtime, replacing the entire machine should not be the only option.
United Lithium Solutions recently received a Slinger Bag battery that had become difficult to charge and would only operate for a short period before shutting down. Since replacement batteries were unavailable, the customer sent the original battery to our Battery Revival Center for inspection and rebuilding.
Original Battery Specifications
The battery was labeled with the following specifications:
- Model: KMD-SB-4660
- Nominal voltage: 14.4V
- Original capacity: 6.6Ah
- Energy rating: 95Wh
- Standard charging current: 2A
- Continuous discharge rating: 15A
- Battery chemistry: Rechargeable lithium-ion
- Cell count: 12
- Configuration: 4S3P
- Cell size: 18650
A 4S3P battery contains four cell groups connected in series, with three cells connected in parallel in each group. This arrangement produces the required 14.4V nominal voltage while increasing the battery’s total capacity.
What We Found Inside
After carefully opening the original housing, we confirmed that the battery contained 12 cylindrical lithium-ion cells.
The original cells appeared to be generic cells rather than premium name-brand cells. The customer reported that the battery previously took a long time to charge, delivered reduced runtime, and eventually stopped charging altogether.
These symptoms are often caused by aging cells, imbalance between cell groups, or increased internal resistance.
For a proper rebuild, we replace the entire matched set of cells rather than mixing new cells with older ones. Mixing cells of different ages and conditions can create additional imbalance and lead to premature failure.
Upgrading From 6.6Ah to Approximately 9Ah
The original battery was rated at 6.6Ah. Our rebuild uses 12 matched 3000mAh 18650 lithium-ion cells in the same 4S3P configuration.
Three 3000mAh cells connected in parallel provide approximately:
3 × 3000mAh = 9000mAh, or 9Ah
This increases the rated battery capacity from 6.6Ah to approximately 9Ah.
That represents about a 36% increase in capacity compared with the original battery rating.
The rebuilt battery remains:
- 14.4V nominal
- 16.8V fully charged
- Compatible with the original housing
- Compatible with the original mounting bracket
- Compatible with the original charging and discharge connections, provided they pass inspection
The completed battery is expected to provide approximately 130Wh of energy compared with the original 95Wh rating.
Actual runtime will vary depending on ball speed, feed rate, elevation settings, temperature, battery condition, and machine usage.
Our Slinger Bag Battery Rebuild Process
Each battery is inspected before rebuilding begins.
Our process includes:
- Testing the battery voltage, charging port, output connector, and internal electronics.
- Carefully opening the original battery housing.
- Removing the original 12-cell battery assembly.
- Inspecting the BMS, wiring, connectors, and protective components.
- Building a new matched 4S3P lithium-ion cell pack.
- Installing new nickel connections and protective insulation.
- Reassembling the battery inside the original housing.
- Charging, balancing, and discharge testing the completed pack.
- Completing a final quality-control inspection before return shipping.
Whenever possible, we reuse the original battery housing, mounting system, connectors, wiring, and compatible battery-management electronics.
Rebuilding Versus Buying a Replacement
A new original replacement battery has been listed for approximately $99 when available. However, the replacement retains the original 6.6Ah capacity.
Our rebuilt version increases the battery to approximately 9Ah while allowing the customer to continue using the original housing and mounting system.
Available Service Options
Standard 9Ah Battery Rebuild: $99.99
Priority 9Ah Battery Rebuild: $120.00
Return shipping is calculated separately.
Additional charges may apply if the battery has a damaged BMS, charging port, connector, wiring harness, or housing. Any additional work is quoted for approval before it is completed.
Common Slinger Bag Battery Problems
A battery rebuild may be appropriate if your Slinger Bag battery:
- No longer charges
- Takes an unusually long time to charge
- Provides very limited runtime
- Shuts down unexpectedly
- Drains quickly after charging
- Is unavailable as a replacement
- Needs a higher-capacity upgrade
Do not continue using or charging a battery that is swollen, leaking, punctured, excessively hot, burned, or physically damaged.
Mail-In Slinger Bag Battery Rebuild Service
To begin a rebuild, complete our Battery Revival Service Authorization form and send your original battery to our Las Vegas service center.
United Lithium Solutions LLC
4856 Judson Ave., Suite 155
Las Vegas, NV 89115
Phone: 775-507-3288
Email: sales@unitedlithium.us
No paid rebuilding work is performed until the battery has been inspected and the final service has been approved.
United Lithium Solutions is an independent battery rebuilding company and is not affiliated with or endorsed by Slinger Bag. Brand names and model numbers are used only to identify compatible equipment.